I've just enabled profile avatars for us, here -- at least for the moment. They're still totally optional, but they're fun. I uploaded a 14K animated .GIF for myself as a test, and it works a treat. (However, if the tick-tock-tail kitty is too distracting or whatever, I'm happy to change it. As I said, this is a test; we'll see how it goes.)
Avatar size limits are 20x20 px minimum, and 100x100 px maximum. Size limit is 20480 bytes (20 Kb). I didn't see any format restrictions, but I'm guessing acceptable formats are .JPG, .GIF, .PNG, etc... basic WWW stuff. Little snippets of Flash (.SWF) probably won't work.
Click "post reply" with feedback! Thanks and enjoy!