Arch this is the best rationale you mentioned. It would be so cool to see more intelligent posts on here and less flame-warring. Another neat aspect of this is this: no one sees the avatar you pick except you, unless you post a screen shot. So it would be cool to see who respects you when people place SS's.

The only real thumbs-down I can think of is that you'd have scores upon scores of newbies asking "Can you put my picture in it?" But I think it's a very good idea, and I hope it gets implemented soon.