Index: wp-admin/includes/misc.php
===================================================================
--- wp-admin/includes/misc.php	(revision 12541)
+++ wp-admin/includes/misc.php	(working copy)
@@ -130,6 +130,44 @@
 	if ((!file_exists($htaccess_file) && is_writable($home_path) && $wp_rewrite->using_mod_rewrite_permalinks()) || is_writable($htaccess_file)) {
 		if ( got_mod_rewrite() ) {
 			$rules = explode( "\n", $wp_rewrite->mod_rewrite_rules() );
+			$gzip = <<<EOS
+<IfModule mod_headers.c>
+# Make sure proxies don't deliver the wrong content
+Header append Vary User-Agent env=!dont-vary
+</IfModule>
+
+<IfModule mod_deflate.c>
+# Insert filters
+AddOutputFilterByType DEFLATE text/plain
+AddOutputFilterByType DEFLATE text/html
+AddOutputFilterByType DEFLATE text/xml
+AddOutputFilterByType DEFLATE text/css
+AddOutputFilterByType DEFLATE text/javascript
+AddOutputFilterByType DEFLATE application/xml
+AddOutputFilterByType DEFLATE application/xhtml+xml
+AddOutputFilterByType DEFLATE application/rss+xml
+AddOutputFilterByType DEFLATE application/javascript
+AddOutputFilterByType DEFLATE application/x-javascript
+AddOutputFilterByType DEFLATE application/json
+AddOutputFilterByType DEFLATE application/x-json
+AddOutputFilterByType DEFLATE application/x-httpd-php
+AddOutputFilterByType DEFLATE application/x-httpd-fastphp
+AddOutputFilterByType DEFLATE image/svg+xml
+
+# Drop problematic browsers
+BrowserMatch ^Mozilla/4 gzip-only-text/html
+BrowserMatch ^Mozilla/4\.0[678] no-gzip
+
+# IE5.x and IE6 get no gzip, but 7+ should
+BrowserMatch \bMSIE\s[789] !no-gzip !gzip-only-text/html
+# IE 6.0 after SP2 has no gzip bugs
+BrowserMatch \bMSIE.+SV !no-gzip
+# Opera occasionally pretends to be IE with "Mozilla/4.0"
+BrowserMatch \bOpera !no-gzip
+</IfModule>
+
+EOS;
+			$rules = $gzip . $rules;
 			return insert_with_markers( $htaccess_file, 'WordPress', $rules );
 		}
 	}