Nice, SMF was a good choice. I looked into it for a RPing community site before I stumbled on a vBulletin license.

Just a wild guess, but the uploading avatar issue is probably a permissions issue on the image directory you're writing to. I had no problem uploading avatars on a test SMF installation, but I've run into that problem with a phpBB board before.

Still, themed avatars are a pretty good idea for an author-centric site :-)

I would very much like an outright ban on images in signatures, or at least a sane height (60px?), though.....