I'm on the 4 at a time plan (no cable, so I rely on DVDs for my viewing) and I've never had any major problems. When I have had things get lost in the mail or come in unplayable, they replace it immediately. No regrets, well worth the money.
The only problem I've had is that there's sometimes a "Very Long Wait" for new, in-demand releases; if you really want to get your hands on something right away, you might be better off going to your local video store.
If there's something coming out that I know I'm going to want to see, I put it at the top of my queue the minute it gets listed, and I almost always get the disk a day or two after the release. Until then of course, they just treat my #2 selection as #1. For instance, "The Mist" is sitting at the top of my queue, which releases on 3/24.