Yale actually has a pretty odd application review process. The Dean of Admissions reviews all applications at least once and weeds out definite rejections - I'm guessing this is about 75% of the applicant pool. The remaining applications are each reviewed by 3 different faculty members (out of a pool of 60 faculty), and rated from 2 to 4 by each professor. Any apps that get all 4s, for a total score of 12, are immediately accepted. 11s are kept on hold and are generally accepted after all the apps are reviewed, 10s and below are rejected. Legacy candidates (sons/daughters of alums) get a bonus +1 to their final score. The crazy thing is that there is really no consistency between the grading of various faculty, and because every app is only reviewed by 3 of the 60 total reviewers, you could get screwed or picked up depending on which side of the bed your reviewers got up on that morning.
The other thing is that about 80% of the students accepted by Yale end up going there - compared to 30% at Columbia and 40% at Stanford (Not sure about Harvard).
Anyways, I've met a couple yale admits - most of them applied really really early. I'm still waiting, but I will probably take my name off the list if I don't hear before the end of April.