I've been with Netflix about three years now and have had a very positive experience overall. Their delivery has always been timely and the price is worth it.
The entire time I've been with them I've only received two discs that could not play. One was too scratched up (an Alias disc, I forget what season and a Babylon 5 disc that was cracked). Both discs were replaced quickly and I was even given an additional disc to view for my trouble.