On my bulletin board, I allow avatars (80 x 80 pixels, under 3K, non-animated), and attachments of small, unamimated images. There’s a reason why, though; it’s an urban planning-related site, and sometimes we need to show examples of good or bad development somewhere, or an image of a project a user is working on.
Then again, I’ve only got about 700 members and 100,000 posts. If Cyburbia ever approached SDMB-type user levels and traffic, the avatars would go bye-bye, and image attachments would hit the dust; it’s the IMG tag or nothing.
On the SDMB, it’s substance over style. I like it that way. Please, no k-rad KeWl anime avatars with gamerZZZ-style dark green text on a black background that PWnssS!!!1!!! 420 2600 69 420 2600 69 420 2600 69!!! … uhh … sorry. Got carried away.