I just upgraded from 2.0.11 to 2.3 and now my categories are missing as well as the author of the post, however, they appear to remain just fine in the database.
Have a look: http://www.finlandforthought.net
Notice that all my old posts are listed as "uncategorized", except for the recent posts I've written since the upgrade, which are filed under "12". And notice that the post author's name (there are several authors on this blog) is missing from the post. Also notice there are no categories on my sidebar, only one listed as "12".
When I ran upgrade, WP threw a bunch of database errors, yet the upgrade appeared to work. I'm guessing that the database upgrade to 2.3 had failed - Is there a way I can manually check this? Like I said, all the categories and users in my database appear to be just fine.
Just a note: I'm using MySQL v5.0.x, and all my plugins are disabled except Akismet.
Any ideas what the hell went wrong? :-) thanks!!!!!!