Wow, that sounds like a really bad innovation for HBS; the other way in used to require 2-3 years of high-end consulting work, or 4+ years of normal work.
They're bigger than most business schools already (900 students in the class?). Why are they doing this?
I've had a couple of friends that were accepted in 2009, and they speculated the 2+2 program had as high as a 30% acceptance rate in its inaugural year since it wasn't well publicized.
That's my guess.