When I first returned, I noticed that some people had avatars, and others didn't. Most of the people with avatars had corrupted ones.
Case and point: Look at Evil. Evil has a (corrupted) avatar, but (s)he has not been active since December 06, 2009, 02:16:09, which was before the switch. As you can see, (s)he did not yet set up his/her avvie back up.
Mine was not here when I arrived, so I reuploaded. Mine looks fine now. I'll bet most of us with okay avatars reuploaded, and all of us with corrupted ones already had them when they arrived. Also, it seems that the GIFs are the ones that got corrupted, and the PNGs are the ones that didn't transfer.
Also in clear absence are attachments and the favicon. But that seems to be it.