I have participated on forums for a long time. I mostly frequent forums that have to do with beliefs and politics.
For the most part they are enjoyable. I like being able to share my views and show off some of my intellectual side in debate. I love discussing beliefs, interesting ideas, etc. It's definitely a plus to get into topics and details that you normally wouldn't get into in real life. But, I also think there is a downside to being on debate forums too much. At least according to some people who I've known to quit forums (or take a break from it) after a while, some of the negativity on forums can carry over into real life. The negativity I'm referring to is becoming too defensive from having to always defend your views against skeptics and others. But then again, this all depends on the environment of the forum and the types of debate.
I've been on forums for a while but not from the earliest days. I've been on AF.org (a truly horrible atheist forum run by the scum of the earth .. in my unbiased opinion); agnosticsinternational.org (nice place but a ghost town in terms of usage); another agnostic site which was more a dating site for religious non's which was spoiled by the always loud and rude simple minded atheists; another european site called Ship of Fools which was probably more Christian focused but not in a very churchy way; AtheistDiscussion.org which was the best atheist site managed to find but still dominated by the simple minded (along with a number of other fine people); and finally the BioLogos Christian focused forums which is the only one I visit regularly any more. Oh and I managed to hang for a short while at the old William Lane Craig forum on Reasonable Faith but that soon came to feel like senseless self abuse.
An agnostic site would be ideal but unfortunately they never seem well attended. People prefer Jerry Springer I guess.
You are probably right about that. I at least thought that branding as a non-partisan environment would at least get the politics section going but that has not been the case. A lot of people may like the political and ideological divides just as you stated!
The two sites that I have visited a lot, besides this one, is DebatingChristianity.com and Religiousforums.com. The first one is big on debate. BUT, it was my experience on these sites, especially in the politics section, that drove me to start my own site.