Not too long ago, I posted in the Suggestion Box forum that it would be cool to be able to have a small number of different avatars available... my idea was you could have one for each mood you wanted to use in a post. You could make it easier to be clear about when you were trying to be amusing, and when you were serious, for example.

I can only imagine what people who animate and change their avatars a lot would do with that kind of power.