Yes, a couple things that I have noticed:
Avatars are now all displayed at 96x96 in threads, so unlike on the legacy themes, there is no support for avatars with portrait dimensions anymore. On profile pages, however, they seem to display at double that size, so 192x192. That would probably be my suggestion for a minimum size now.
Also, the file size restrictions seem to have changed. I was able to upload an avatar the other day that was over 10x the size of the previous 50KB limit, and it worked perfectly fine. That's one of the reasons I asked the person above to let me know if that avatar uploads ok for them, because it is also very large compared to the previous requirements.