Turns out that during my recent upgrade to the forum software, I managed to break avatar uploads, and it looks like a few of you have run into problems with it. The permissions on the folder where the avatars are stored were not set correctly, so the avatars never got written to disk.

It's fixed now, so if you've tried to upload an avatar in the last few days and it didn't work, try again and it should be fine. Contact me if you're still having problems.