Google+ has a very specific niche at the moment: Groups of specialized hobbyists who want a platform that's a hybrid between a microblog service and a message b

Google+ has a very specific niche at the moment: Groups of specialized hobbyists who want a platform that's a hybrid between a microblog service and a message board. I know that it's currently the center of the indie tabletop RPG world, for instance, and I think the same is true of at least some other similar communities. I don't think it'll ever replace Facebook, but it could certainly make phpBB obsolete.