I hang around the Escapist a lot, but I'm not very active in the forums. If I didn't like the shows and reviews here, I probobly wouldn't bother at all. The same can be said for most sites I frequent.
The only exception was Bungie.net (The Flood, to be specific). The only reason I went there initially was to check out the awesome stat - tracking system they had for Halo 3 multiplayer (it was pretty in depth for its time... maybe it still is actually, I haven't played online multiplayer in a long while).
I can't remember how, but I got drawn into The Flood (off topic forums - in Bnet, that meant everything not directly linked to the Halo games) and was pretty active for a couple of years. It was a really nice forum too... sophisticated without being stuck up, friendly without being overbearing, and the mods were pretty lax too (with the exception of the "Keep it Clean" era - although that was almost justified). I outgrew it a while ago though, but I go back every so often for old times sake.