Recently when i was working on a wordpress project with a premium theme i found bug in wordpress 2.8.
Most of the premium themes use get_categories() function in there functions.php for better management of the plugin from the theme option page at the admin.
But when get_categories() function is called in the functions.php no result are shown.
If you want to get solution for this problem then this problem is solved in the wordpress 2.8.1
Also some other bugs from the wordpress 2.8 are also removed
Check this on wordpress
and update your blog to wordpress 2.8.1