Index: wp-includes/link-template.php
===================================================================
--- wp-includes/link-template.php	(revision 6326)
+++ wp-includes/link-template.php	(working copy)
@@ -226,7 +226,7 @@
 	}
 }
 
-function get_feed_link($feed='rss2') {
+function get_feed_link($feed = '') {
 	global $wp_rewrite;
 	$do_perma = 0;
 	$feed_url = get_option('siteurl');
@@ -239,13 +239,16 @@
 			$permalink = $wp_rewrite->get_comment_feed_permastruct();
 		}
 
-		if ( 'rss2' == $feed )
+		if ( get_default_feed() == $feed )
 			$feed = '';
 
 		$permalink = str_replace('%feed%', $feed, $permalink);
 		$permalink = preg_replace('#/+#', '/', "/$permalink");
 		$output =  get_option('home') . user_trailingslashit($permalink, 'feed');
 	} else {
+		if ( empty($feed) )
+			$feed = get_default_feed();
+
 		if ( false !== strpos($feed, 'comments_') )
 			$feed = str_replace('comments_', 'comments-', $feed);
 
@@ -255,15 +258,18 @@
 	return apply_filters('feed_link', $output, $feed);
 }
 
-function get_post_comments_feed_link($post_id = '', $feed = 'rss2') {
+function get_post_comments_feed_link($post_id = '', $feed = '') {
 	global $id;
 
 	if ( empty($post_id) )
 		$post_id = (int) $id;
 
+	if ( empty($feed) )
+		$feed = get_default_feed();
+
 	if ( '' != get_option('permalink_structure') ) {
 		$url = trailingslashit( get_permalink($post_id) ) . 'feed';
-		if ( 'rss2' != $feed )
+		if ( $feed != get_default_feed() )
 			$url .= "/$feed";
 		$url = user_trailingslashit($url, 'single_feed');
 	} else {
@@ -277,6 +283,119 @@
 	return apply_filters('post_comments_feed_link', $url);
 }
 
+/** post_comments_feed_link() - Output the comment feed link for a post.
+ *
+ * Prints out the comment feed link for a post.  Link text is placed in the
+ * anchor.  If no link text is specified, default text is used.  If no post ID
+ * is specified, the current post is used.
+ *
+ * @package WordPress
+ * @subpackage Feed
+ * @since 2.4
+ *
+ * @param string Descriptive text
+ * @param int Optional post ID.  Default to current post.
+ * @return string Link to the comment feed for the current post
+*/
+function post_comments_feed_link( $link_text = '', $post_id = '', $feed = '' ) {
+	$url = get_post_comments_feed_link($post_id, $feed);
+	if ( empty($link_text) )
+		$link_text = __('Comments Feed');
+
+	echo "<a href='$url'>$link_text</a>";
+}
+
+function get_author_feed_link( $author_id, $feed = '' ) {
+	$author_id = (int) $author_id;
+	$permalink_structure = get_option('permalink_structure');
+
+	if ( empty($feed) )
+		$feed = get_default_feed();
+
+	if ( '' == $permalink_structure ) {
+		$link = get_option('home') . '?feed=rss2&amp;author=' . $author_id;
+	} else {
+		$link = get_author_posts_url($author_id, $author_nicename);
+		$link = trailingslashit($link) . user_trailingslashit('feed', 'feed');
+	}
+
+	$link = apply_filters('author_feed_link', $link);
+
+	return $link;
+}
+
+/** get_category_feed_link() - Get the feed link for a given category
+ *
+ * Returns a link to the feed for all post in a given category.  A specific feed can be requested
+ * or left blank to get the default feed.
+ *
+ * @package WordPress
+ * @subpackage Feed
+ * @since 2.4
+ *
+ * @param int $cat_id ID of a category
+ * @param string $feed Feed type
+ * @return string Link to the feed for the category specified by $cat_id
+*/
+function get_category_feed_link($cat_id, $feed = '') {
+	$cat_id = (int) $cat_id;
+	
+	$category = get_category($cat_id);
+	
+	if ( empty($category) || is_wp_error($category) )
+		return false;
+
+	if ( empty($feed) )
+		$feed = get_default_feed();
+
+	$permalink_structure = get_option('permalink_structure');
+
+	if ( '' == $permalink_structure ) {
+		$link = get_option('home') . "?feed=$feed&amp;cat=" . $cat_id;
+	} else {
+		$link = get_category_link($cat_id);
+		if( $feed == get_default_feed() )
+			$feed_link = 'feed';
+		else
+			$feed_link = "feed/$feed";
+		
+		$link = trailingslashit($link) . user_trailingslashit($feed_link, 'feed');
+	}
+
+	$link = apply_filters('category_feed_link', $link, $feed);
+	
+	return $link;
+}
+
+function get_tag_feed_link($tag_id, $feed = '') {
+	$tag_id = (int) $tag_id;
+
+	$tag = get_tag($tag_id);
+
+	if ( empty($tag) || is_wp_error($tag) )
+		return false;
+
+	$permalink_structure = get_option('permalink_structure');
+
+	if ( empty($feed) )
+		$feed = get_default_feed();
+
+	if ( '' == $permalink_structure ) {
+		$link = get_option('home') . "?feed=$feed&amp;tag=" . $tag->slug;
+	} else {
+		$link = get_tag_link($tag->term_id);
+		if ( $feed == get_default_feed() )
+			$feed_link = 'feed';
+		else
+			$feed_link = "feed/$feed";
+		$link = $link . user_trailingslashit($feed_link, 'feed');
+	}
+
+	$link = apply_filters('tag_feed_link', $link, $feed);
+
+	return $link;
+}
+
 function get_edit_post_link( $id = 0 ) {
 	$post = &get_post( $id );
 
Index: wp-includes/author-template.php
===================================================================
--- wp-includes/author-template.php	(revision 6326)
+++ wp-includes/author-template.php	(working copy)
@@ -366,7 +366,7 @@
 	$defaults = array(
 		'optioncount' => false, 'exclude_admin' => true,
 		'show_fullname' => false, 'hide_empty' => true,
-		'feed' => '', 'feed_image' => '', 'echo' => true
+		'feed' => '', 'feed_image' => '', 'feed_type' => '', 'echo' => true
 	);
 
 	$r = wp_parse_args( $args, $defaults );
Index: wp-includes/classes.php
===================================================================
--- wp-includes/classes.php	(revision 6326)
+++ wp-includes/classes.php	(working copy)
@@ -599,7 +599,7 @@
 			if ( empty($feed_image) )
 				$link .= '(';
 
-			$link .= '<a href="' . get_category_rss_link( 0, $category->term_id, $category->slug ) . '"';
+			$link .= '<a href="' . get_category_feed_link($category->term_id, $feed_type) . '"';
 
 			if ( empty($feed) )
 				$alt = ' alt="' . sprintf(__( 'Feed for all posts filed under %s' ), $cat_name ) . '"';
Index: wp-includes/deprecated.php
===================================================================
--- wp-includes/deprecated.php	(revision 6326)
+++ wp-includes/deprecated.php	(working copy)
@@ -729,4 +729,24 @@
 	return $cat->name;
 }
 
+
+function comments_rss_link($link_text = 'Comments RSS', $commentsrssfilename = 'nolongerused') {
+	post_comments_feed_link($link_text);
+}
+
+function get_category_rss_link($echo = false, $cat_ID, $category_nicename) {
+	$link = get_category_feed_link($cat_ID, $feed = 'rss2');
+
+	if ( $echo )
+		echo $link;
+	return $link;
+}
+
+function get_author_rss_link($echo = false, $author_id, $author_nicename) {
+	$link = get_author_feed_link($author_id);
+	if ( $echo )
+		echo $link;
+	return $link;
+}
+
 ?>
\ No newline at end of file
Index: wp-includes/feed.php
===================================================================
--- wp-includes/feed.php	(revision 6328)
+++ wp-includes/feed.php	(working copy)
@@ -5,11 +5,14 @@
 	return apply_filters('get_bloginfo_rss', convert_chars($info));
 }
 
-
 function bloginfo_rss($show = '') {
 	echo apply_filters('bloginfo_rss', get_bloginfo_rss($show));
 }
 
+function get_default_feed() {
+	return apply_filters('default_feed', 'rss2');
+}
+
 function get_wp_title_rss($sep = '&#187;') {
 	$title = wp_title($sep, false);
 	if ( is_wp_error( $title ) )
@@ -97,86 +100,10 @@
 	echo $comment_text;
 }
 
-
-function comments_rss_link($link_text = 'Comments RSS', $commentsrssfilename = 'nolongerused') {
-	$url = get_post_comments_feed_link();
-	echo "<a href='$url'>$link_text</a>";
-}
-
-
 function comments_rss($commentsrssfilename = 'nolongerused') {
 	return get_post_comments_feed_link();
 }
 
-
-function get_author_rss_link($echo = false, $author_id, $author_nicename) {
-	$auth_ID = (int) $author_id;
-	$permalink_structure = get_option('permalink_structure');
-
-	if ( '' == $permalink_structure ) {
-		$link = get_option('home') . '?feed=rss2&amp;author=' . $author_id;
-	} else {
-		$link = get_author_posts_url($author_id, $author_nicename);
-		$link = trailingslashit($link) . user_trailingslashit('feed', 'feed');
-	}
-
-	$link = apply_filters('author_feed_link', $link);
-
-	if ( $echo )
-		echo $link;
-	return $link;
-}
-
-/** get_category_feed_link() - Get the feed link for a given category
- *
- * Returns a link to the feed for all post in a given category.  A specific feed can be requested
- * or left blank to get the default feed.
- *
- * @package WordPress
- * @subpackage Feed
- * @since 2.4
- *
- * @param int $cat_id ID of a category
- * @param string $feed Feed type
- * @return string Link to the feed for the category specified by $cat_id
-*/
-function get_category_feed_link($cat_id, $feed = 'rss2') {
-	$cat_id = (int) $cat_id;
-	
-	$category = get_category($cat_id);
-	
-	if ( empty($category) || is_wp_error($category) )
-		return false;
-	
-	$permalink_structure = get_option('permalink_structure');
-
-	if ( '' == $permalink_structure ) {
-		$link = get_option('home') . "?feed=$feed&amp;cat=" . $cat_id;
-	} else {
-		$link = get_category_link($cat_id);
-		if( 'rss2' == $feed )
-			$feed_link = 'feed';
-		else
-			$feed_link = "feed/$feed";
-		
-		$link = trailingslashit($link) . user_trailingslashit($feed_link, 'feed');
-	}
-
-	$link = apply_filters('category_feed_link', $link, $feed);
-	
-	return $link;
-}
-
-
-function get_category_rss_link($echo = false, $cat_ID, $category_nicename) {
-	$link = get_category_feed_link($cat_ID, $feed = 'rss2');
-
-	if ( $echo )
-		echo $link;
-	return $link;
-}
-
-
 function get_the_category_rss($type = 'rss') {
 	$categories = get_the_category();
 	$tags = get_the_tags();
@@ -215,32 +142,6 @@
 	echo get_the_category_rss($type);
 }
 
-function get_tag_feed_link($tag_id, $feed = 'rss2') {
-	$tag_id = (int) $tag_id;
-
-	$tag = get_tag($tag_id);
-
-	if ( empty($tag) || is_wp_error($tag) )
-		return false;
-
-	$permalink_structure = get_option('permalink_structure');
-
-	if ( '' == $permalink_structure ) {
-		$link = get_option('home') . "?feed=$feed&amp;tag=" . $tag->slug;
-	} else {
-		$link = get_tag_link($tag->term_id);
-		if ( 'rss2' == $feed )
-			$feed_link = 'feed';
-		else
-			$feed_link = "feed/$feed";
-		$link = $link . user_trailingslashit($feed_link, 'feed');
-	}
-
-	$link = apply_filters('tag_feed_link', $link, $feed);
-
-	return $link;
-}
-
 function html_type_rss() {
 	$type = get_bloginfo('html_type');
 	if (strpos($type, 'xhtml') !== false)
Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 6326)
+++ wp-includes/functions.php	(working copy)
@@ -861,7 +861,7 @@
 	$feed = preg_replace( '/^_+/', '', $feed );
 
 	if ( $feed == '' || $feed == 'feed' )
-		$feed = 'rss2';
+		$feed = get_default_feed();
 
 	$hook = 'do_feed_' . $feed;
 	do_action( $hook, $wp_query->is_comment_feed );
Index: wp-includes/category-template.php
===================================================================
--- wp-includes/category-template.php	(revision 6326)
+++ wp-includes/category-template.php	(working copy)
@@ -247,7 +247,7 @@
 		'order' => 'ASC', 'show_last_update' => 0,
 		'style' => 'list', 'show_count' => 0,
 		'hide_empty' => 1, 'use_desc_for_title' => 1,
-		'child_of' => 0, 'feed' => '',
+		'child_of' => 0, 'feed' => '', 'feed_type' => '',
 		'feed_image' => '', 'exclude' => '',
 		'hierarchical' => true, 'title_li' => __('Categories'),
 		'echo' => 1
Index: wp-content/themes/default/sidebar.php
===================================================================
--- wp-content/themes/default/sidebar.php	(revision 6326)
+++ wp-content/themes/default/sidebar.php	(working copy)
@@ -51,7 +51,7 @@
 				</ul>
 			</li>
 
-			<?php wp_list_categories('show_count=1&title_li=<h2>Categories</h2>'); ?>
+			<?php wp_list_categories('show_count=1&feed=Atom&feed_type=atom&title_li=<h2>Categories</h2>'); ?>
 
 			<?php /* If this is the frontpage */ if ( is_home() || is_page() ) { ?>
 				<?php wp_list_bookmarks(); ?>