In my case, it's a combination of boredom and lack of people to have certain types of conversation with. I have friends here in Japan, but none of them like video games and they're not really well versed in American culture (either because they're Japanese or English speakers from outside the States). This is a great outlet just for talking about the normal, everyday stuff I would talk about with people back home. It's no coincidence that I was not a particularly prolific poster back in the States, but as soon as I found EB (and found that it wasn't blocked at work, which I hope stays that way) I began posting more and more. Expect my number of daily posts to diminish as soon as I go back home.
I won't lie, though; sometimes I post here because there's something I have to do which I don't want to do, and this serves as a form of procrastination. I know it's unhealthy, but I do it anyway. :/