On: Led by Stanford’s 5%, Top Colleges’ Acceptance Rates Hit New Low

And doesn't this mean also that many students are getting many acceptances and turning most of them down?

That, of course, should lead to higher acceptance rates again so that colleges don't end up with an empty incoming class.

Colleges actually accept larger numbers than they can have in a class (i.e 1,800 for a 1,000 person class). Students will get in off the waitlist, but I don't think that affects the overall admission percentages

My undergrad ( Texas State University ) had the problem recently where they accepted the higher number, expecting the smaller number, and then most of the higher number actually attended :P It was the largest freshmen class in the school's history and let to a more... relaxed policy for sophomores living off campus.