Hmm, I don't think that's necessarily true. For new releases Netflix often doesn't have enough to go around and has to make people wait. I bet efficiency there is appreciated.
Netflix notoriously throttles heavy users. Their largest expense is postage. I'm sure their calculus is more complex, but if they had to pick an extreme, i'd wager that they'd pick the guy who has had the same 3 discs sitting on his table for the last month.
For some reason, I would rather watch Simpsons reruns than some movie I've never seen.
(I returned one disk today that has been on my coffee table for two months. I just couldn't get excited enough to watch the movie, and I was tired of looking at the disk.)
