A lot of mention has been made of the seriousness of Stack Overflow (and presumably Server Fault). Would it be a good idea to turn smilies :-) into actual images as per phpBB in questions and answers?
I would say no. I believe a humorous answer now and then is a good thing and perfectly acceptable. However, I would see adding graphical smilies as encouragement to use them and I don't think its behavior that should be encouraged. It doesn't need to be discouraged, but I wouldn't want it to be encouraged.
If you really care about smilies that much, use Firefox and write your own smiley-to-image converter in Greasemonkey.
I love getting information from SO. Apart from fun questions, smileys always iritate me (even ASCII character based ones). If you want to be sarcastic, hint that something is not to be taken seriously, I suggest rephrasing in most cases. There is the odd case of humor - which most the times speaks for itself. And do not forget people with non English background.
But most of all, inline graphics are most distracting.
So please do not add this feature.