To echo what others have said, I've been very happy with Netflix's service.
I'm on the two discs at a time plan, and besides "popular" material, I've rented some rather obscure dvds and haven't had any problems. They carry a wide selection of Doctor Who (everything that has been released in the states is available there. I'm not sure what the complaint above was about having more of the released Doctor Who on there, though there's certainly more in the UK than in the US), which was the reason I signed up in the first place.
I know of some who get dvds and watch them the same day and return them that night. I've heard of "throttling" and stuff like that, and it concerned me enough when I signed up that I kept a spreadsheet with the dates I sent discs back and when Netflix said they were sent, and when I received them. After a few months, I realized it was completely pointless, because they always came through exactly the same way. I send the disc. They receive it the next day and ship the next disc that same day, and I get it the next day. So if I return a disc Tuesday, I get its replacement on Thursday. Weekends don't count, since they're Monday through Friday only.
Somehow, they even receive and ship on holidays. Three times now I've returned a disc that they should not have received when they did due to a postal holiday, whether it's Christmas or Presidents' day or whatever, and they have indeed received em and shipped out the new one that same day, so I still get them the day after the holiday.
I don't know how they do it, and don't care, I just know I get my discs.
Now, with all that said, I have had three "issues" ... One was the disc "Monster Squad" ... It locked up at the same spot no matter what dvd player I used (tried a few). Cleaning didn't help. I went on their site and let them know about the issue. They sent a replacement that day, I had it the next, and sent both copies back. The replacement played just peachy keen.
The other was a two-disc set. I don't remember what it was ... some tv show. Anyway, they didn't arrive when they should have, and didn't show up the next day either. I did one of those "missing disc" buttons on their site and they shipped out replacements the same day. The originals never did show up, must have gotten lost in the mail.
Considering the hundreds of discs I've gone through with them, three isn't bad at all.
Now, with all that said, I generally do two discs a week, as I don't have time for more ... usually. Sometimes I can go through four a week, but not very often. Of course, YMMV.