I'm seeing that a lot of people have "lost" their comments. I seem to have lost my categories. Old entries still have the categories listed next to them in the Entries screen and the category archives are intact, but upon entering a new entry, there are no categories listed in the pulldown menu. Eek!

This was after upgrading from 3.16 to 3.2.

Sorted this out myself. It may be of some help to people who have lost comments, but I'm no mySQL expert, so don't quote me.

I ran CocoaMySQL (but you could run phpSQLadmin or some other similar tool) to look at my tables, and found that under category_parent, everything was set to "NULL". When creating a new category, this was set to "0", so I changed all of the other categories to "0" and they magically reappeared in MT.

You could try this on your comments table and see what happens. Back up or export first, though...