Symptom: After upgrading to Wordpress 2.7, users who have the wp-sticky plugin active may see the following error:
Fatal error: Cannot redeclare is_sticky() (previously declared in /home/user/public_html/wp-includes/post.php:756) in /home/user/public_html/wp-content/plugins/wp-sticky/wp-sticky.php on line 150
Cause: Wordpress 2.7 allows the tagging of a post as sticky without the plugin (under the Publish menu, choose Edit, then Visibility)
Solution: Disable or delete the wp-sticky plugin by removing it from the plugins directory, or upgrade the wp-sticky plugin to v1.40, which is compatible with Wordpress 2.7.