The Team registration fee is $10K, so I suppose you can say we are "serious" ;-)
The Carnegie Mellon Team has great experience in the Rover department. But I think getting the rover safely on the surface is the real challenge. The CMU team is the only one that has officially announced their participation, as far as I've heard. But I'm sure we'll find the field is quite full once the X PRIZE Foundation reveals the registered teams.
At present, Odyssey Moon is the only fully registered team (read: $10,000 paid in full).
Google and the X Prize Foundation actually have to approve a team's application after reviewing detailed preliminary project plans, budget plans, etc. Even they don't think there will be any more than a dozen or so teams.