I'll throw in why I haven't and wouldn't as I haven't answered.
Similar to some of the other answers...
Firstly a big difference in the 3d world is that words are momentary and people forget what is said or move on. Words online once written are there to be seen, unless you go through and delete everything.
A second part to that is that you can choose who you speak to.
Thirdly, I am a different person around different people and that effects what I choose to do and say around them. Online I don't have that luxury. So as far as I'm concerned things can be taken out of context for what I was at the time.
People change, I've been on here for a couple of years now and there are things that I've said when I needed advice, when I wasn't as positive a person (even positive things have been a little stupid now and then) and I didn't want to go to people I saw on a regular basis.
So there we haven't, I'm happy for you guys to see what I look like, but I don't want something out of my control to come back and bite me in the ass. Something that could be meaningless to me and I'd likely never know who was reading what about me. And forming opinions that I couldn't see.