3. There is no strict ranking system. There is the Idiot Hierarchy, which exists purely for amusement, and various other groups with certain conditions for entry. Membership of such groups will not give you access to additional features of the forums.
I think some of these groups do give access to additional features... the birthday group does for that day, right? (And moderator titles like Acolyte are also technically groups as far as I know.) It's definitely not a ranking system though.
Anyway, I think TS666's original question was referring to the Tourist->Neophyte->normal member, which is basically covered by that less-than-10-posts thread. (Tourist = 0-2 posts, Neophyte = 3-9 posts)