I started with Yahoo Answers but gave up on it as it slid downhil. I tried Google Answers, but they cancelled it.
I went to an AOL property that morphed into Propeller, a social news site somewhat like Digg. I gave up on it when they made it almost impossible to submit an article for discussioin and get any level of response to it. You had been allowed to submit an article and send the submission to all your friends list at once. They switched it to a drop-down list where you could only select 5 friends at a time. The result was that only people with nothing else to do in life could get an article onto the front page for discussion.
I came here in the great Answerbag diaspora. I still have my account there. Amazingly, while it’s nearly dromant in new questions, questions I asked there many months ago are now getting new answers daily.
I’m now active here and on Sodahead.com and WhatandWhy.ning.com and have signed up for the Ning.com developers forum. Sodahead is the wild-wild West for political discussion and seems to be very heavily tilted toward right wingers, some of them horribly extreme. They have avowed white supremacists, Aryan Nation folks, skinheads, and this and that right-wing malitia all spouting some pretty hateful speech. But you can definitely talk politics there is you’re hardy enough for it, and there are some fine people there as well who do hear the more moderate voices and appreciate them.