my college roommate works there full time. he's a pretty bright guy.
recently he recommended one of our mutual friends to the company. our friend is pretty close to a genius. smartest kid (in CS) that i've ever met. at CMU, in CS classes, he'd blow away the TA's solutions when it came to benchmarks. for some reason MS rejected him.
so i'd say its pretty hard to get in. even if you're brilliant, its still pretty much a crapshoot.