I've been using gamefly for nearly a year now. Here's how it works. You fill up a queue just like you do with Netflix. You organize it by your most wanted. Naturally, when a smokin hot game releases there's a demand however, if you've had it in your queue in advance of its release you're going to get it fairly quick. If you put it in a few days after then you'll wait a little while. Even still, I put Manhunt II in my queue about a week after release when it was showing "low availabilty." I had two games out at the time (currently the plan I'm on), sent one back and got it about three days later. I'm not complaining. Game turnaround is quick. I'm on the east coast and my turn around averages 2/3 days. Pretty much right on par with Netflix.
Now, if you've got a ton of stuff in your queue and the hot item is at low availability they're going to send you whatever is next in line that's available which is why I organize my queue with my top five or so and leave it at that.
Personally, I love gamefly. Like you say, with games at $50 or $60 a pop it's pretty much the only way to play everything you want to play and they're on top of every new release. If and when you do want to buy something you can just buy it directly from them either via their "keep it" feature or their store. Either way you get all the original packaging and manuals so it's basically like buying brand new. Especially new releases.
Hell, with Xmas coming up you ought to ask people for a membership gift certificate. I actually bought a couple for my nephews this year. They've got em from one month all the way up to a year. Here's the
info. If you can't wait do the free trial.