Even if this might be self-evident, I'd like to make this comment.
It seems that when you know a person any better the avvies mainly enrich your view of them ("Ha, s/he took that kind of avvie, interesting...") but when you're in contact with someone whom you don't actually know so well the avvie (and the screen-name) I think is quite an important thing forming an idea of someone.
Let's make a recent example.
Pitchwife came into the 'Downs and entered a WW-game with an avvie of a Lassie... Looking at the combination it was not so unpredictable almost everyone took him as a female...
Or what has been discussed on
McCaber's avvie here...
But anyway, what I was thinking about putting this thread up was indeed the fact that when you don't know the other person in RL you're discussing with in a forum - or who's posts you read - you form an idea of that person anyway. And as some have said being especially visual people forming their ideas heavily on visual things, I think we all are visual creatures. So it's not only what the others write but also how they present themselves visually (by means of an avvie) that plays a part in our view of others.
If someone uses only "funny avatars" you make certain judgements about that person (surely related to what that person talks), or if someone only uses "artistic" avvies you come up with probably different thoughts... whatever. (Think of the difference of two fictive 'Downers: the other uses only Orlando Bloom avvies and the other uses as avvies only rare pics of some medieval manuscripts...) It is a sum total of many things, but I do think the avvies have a role to play here, which role is not so small one might think.
If you asked me, I would answer that I have never myself thought of my avvie from the perspective of "imago-management"... I've just used ones I've felt are nice or great - or fitting to certain occasion (like this last one jubilating the landing on the Moon 40 years ago).
But sure, being honest, it is also a pic I want to give to others of me and who I am... It's pretty hard to deny that either - whether it is "I love this kind of art" or "my sense of humour appreciates this", "this Tolkien character I find interesting" or whatever. And from this POV also not using an avvie is a statement of one sort... as has been clearly seen from the discussion.
As
Eönwë said: interesting to see two people changing their avvies with this discussion!