I rent anywhere from 16 to 20 discs from Netflix a month. I NEVER wait more than 1 day for shipping. (So, for example, if I send a disc in on Monday they mark it received on Tuesday, and I have a new disc on Wednesday). Now, I do have to wait awhile to get some new releases, but it's not usually toooooo bad.
Here's a tip for you, though. Set up a second queue, which they let you do for another family member in the same household, etc. Designate that queue to get 1 disc at a time and your main queue to get the other two. Now, put ONLY a couple very new releases onto that queue (seriously, put like 1 new movie that you've been waiting for ONLY on it - after it ships, add another). Since they HAVE to send you a disc from that queue now (otherwise you won't be getting the 3 discs at a time you are paying for) and you only have one movie on there you will get it really fast.
This seems to work for most people. I haven't tried it much, I don't watch a lot of "popular" new releases...
EDIT: have to add that if you are getting more than 20 discs a month you must do nothing but watch movies. In the winter I will get 20 discs, and that's mainly because my wife and I will watch TV shows on DVD that we missed last year, etc. 16 is still a movie every other day!
It costs Netflix something like 33cents per movie just in postage, not to mention the envelope and the processing. I read that if you get more than 21 DVDs a month then they start to lose money. This is plenty for MOST customers, and while I agree this should be mentioned in the fine print at least, I don't think it's really that big of a deal. The price is pretty amazing, say 16 movies (keeps you off the heavy user list) would go for +/- $50 at most video stores and we're paying $20! You could always upgrade to a 4 or 5 at a time plan... or watch less movies!