I have been a member of 2 forums, including this one. The first one, my friend introduced me to, it was a private forum of progressive people from my same faith/religious background (a rare combo, unfortunately), and I found it very useful to understand how people reconciled different aspects of their beliefs with the real world and their experiences. It was pretty small and I ended up meeting a huge portion of the people in real life, which was fabulous.
The second one was this one, and I was interested in understanding myself better and improving my interactions with others.
Both forums have had the side effect of also having fun/funny people who are interested in play/fluff, which is refreshing for little breaks from my job (which is great, just everyone needs breaks from time to time).
I actually was really hesitant to join this forum, but maybe if I come across ones that pertain to my different interests/hobbies then I won't be so reluctant in the future.