Thread created to be a sticky with 3.0 issues and resolutions. Please add info as necessary
Problem with Podcasting Plugin by TSG "Call to a member function add_rewrite_tag() on a non-object"
Note plugin author has update.
Problem with HeadSpace2
Problem with Event Calendar, see:
Problem with WP-Ban, see:
Stuck in Maintenance Mode:
Problem with PHP 5.0.5 (Earthlink hosting) and PHP 4.4: