I spend more than 40 hours per week in forums. I'm constantly on GPWA. Now this is something remarkable for me because I didn't participate in any forums before Casino City became involved in GPWA, but the mode of interaction really grew on me. I'm on a lot for work items; reviewing seals, membership applications, moderating, etc., but the boundaries between work and play aren't solid for me. I check in on the weekends to keep up with posts and checking the forum one last time has become part of my bedtime routine (which is killing me because my internet connection is down at home right now!).
Now that I've gotten into this type of interaction I'm also participating in the forum for DragonCrest, the live action roleplaying game that my avatar is from. I used to lurk a lot there but have started posting some and am really getting into it. It is a funny one because there are game events 6 times a year and the game season ends in October and starts again in April. There is a huge spike in posting around the events and then another spike mid-winter as we all start to getting withdrawal symptoms. Don't tell my boss, but I've been sneaking some time in the game forum from the office.
The thing about working on a forum site the fun of it and friendships that evolve really blur the boundaries between work and play.