It is based on number of posts and you can't be demoted (or at least I haven't seen that feature yet. hmmmm.... that could be interesting...).
I don't remember what the hurdle numbers are. I'd have to go deep into the bowels of the system to pull those out.
Serendipity -- could be that you noticed those odd numbers right when we made the new names. Takes the system a bit to catch up and reindex everyone to the right categories.
I have this crazy notion that Carpal Tunnel Candidate comes from the frequency of your posts.
I was a carpal tunnle candidate and now (just recently) I am a forum fanatic. I saw people with less posts then me being forum fanatics when I was a CTC and I have not posted as much lately so thus why I think it has to do with the amount of posting you do. But Tim will have to pop in and clarify this.
I love the suggestions for other titles. Very Cute!