An interesting concept.

However, as the number of reviewers grows, how do you maintain quality?

In the limit, the system becomes one in which anyone can sign up. So how do you maintain quality once the floodgates eventually open?

(Saying: "That won't happen" is not a good answer. There has to be some notion of a reputation system.)

edit: With respect to the argument that the floodgates will not open, how will that occur? What is the model for keeping things a closed community? Nearly every "invite-only" community tends to get blown out after a while.