Over the past year, I've joined several of these MS FaceBook groups, stayed in a few, and posted things from time to time. Like most Facebook groups, there are distinct cultures in them all, recognizable personalities, and the occasional heavy-handed admin. Some of the groups are more serious than others, and only a few are all that active (in terms of posts-per-week).
While I can't say that I've "found the perfect MS group" on Facebook just yet, I do appreciate the way these groups transcend the dynamics of my local MS support group. The groups don't seem controlled by the admins all that much. Instead, it's just folks like you and me posting about what's relevant at the time.