I find that smileys can be a helpful substitute for the tone of voice and facial expression that is missing from the communication when writing - we do not know each other (not well anyway) and can sometimes mistake a brief reply for terseness or coldness, or flippancy for sarcasm. 
I once unintentionally upset someone and would hate to do it again, so I use smilies to make my meaning clear.
It is also helpful for people whocommunicating in a language other than their first, and who may not be aware that they way they word things can appear rude - a smiley would show that was not their intention.
As for anonimity, hopefully my avatar doesn't give away too much of my identity 