What's the problem with emoticons? Used properly and sparingly, they're an important part of internet discourse; voice tone does not transfer well over text, at least not without writing multiple pages of it just to get the point across. Forum posts, even the really long ones, are a lot shorter form than that, and emoticons are occasionally useful. Think about it -- they prevent a lot of flamewars, because they can be the difference between an ad hominem attack, and a harmless joke.
Edit: Think about how books are written. They're full of little comments like "'Nice hat' he said, his voice dripping with sarcasm." Emoticons fill in the "his voice dripping with sarcasm" part a lot better than going Nice hat, or worse, *sarcastically*Nice Hat*sarcastically*. Doesn't "Nice hat XD" just work better?