I've been an Experts Exchange member for about 9 years now. I haven't been very active there for a while, though. I lost a bit of interest in that site since my favorite topic (Delphi) has become less interesting and most questions have been asked before and thus repeat themselves. Still, I've never paid for this site and have earned four t-shirts and a $100 prize from them by answering a lot of other people's questions there. It also gave me enough points to ask a new question there every day for the next 5 years, if I want to.
Then, of course, membership of EE can be free if you earn enough points per month to be recognized as an expert. And to be honest, if they would make every member with over half a million points (like me) a permanent member, I would probably be more interested in EE and less in SO. It's just that I don't want to spend every day on EE trying to earn points so I'm a free member for just another month.