Index: wp-includes/pluggable.php
===================================================================
--- wp-includes/pluggable.php	(revision 14757)
+++ wp-includes/pluggable.php	(working copy)
@@ -103,10 +103,10 @@
 function get_userdata( $user_id ) {
 	global $wpdb;
 
-	if ( ! is_numeric( $user_id ) )
+	if ( ! is_scalar( $user_id ) )
 		return false;
 		
-	$user_id = absint( $user_id );
+	$user_id = max( 0, (int) $user_id );
 	if ( ! $user_id )
 		return false;