I've had quite the opposite experience being a gamefly member for a number of years. As long as I don't have the max number of games out and an empty slot, I always have a new release game shipped the day it releases if it is at the top of my queue with no other released games in my queue. This has never failed for me.
Yup, the trick is having an open slot the day a new game gets shipped. Otherwise, you're stuck in line with everyone else at low availability. I've also heard that they give a higher priority to members who have had a game in their queue for a long time, long before it comes out.
In the few years I've had Gamefly, I've been nothing but happy with it. I've definitely saved a bunch of money. It's great for shorter games that you might not think are worth full price, but want to try anyway. It helps cut down on shipping time if you live near a shipping center - I live in Michigan, my games ship out of Pennsylvania, and it's a two-day trip either way, although lately it's been a little shorter with...I think it's called Fast Return, where they ship you your next game when the Post Office gets yours.