My ISP has complained about the increase in network traffic since I got Netflix, but they haven't given me the opportunity to simply tell them where it's coming from. And frankly, I think they need to join the 21st century and realize that's what people are doing now.
As for Netflix itself, the biggest problem I have is the disparity between what's available on disc and what's available for streaming. When I first signed up, I wrote up a list of about twenty films that I hadn't seen in a long time. Only three of them were actually available, the rest were "disc only". It's actually easier for me to pirate copies of those other films than to deal with shipping discs back and forth.
Along similar lines, some of the content is only available for a limited time. I've seen things disappear from my queue because I didn't know they were going to be taken away. I managed to watch a few others only a day or two before they were being removed because I happened to notice the date on the website, and now they're back to being "disc only".
Someone mentioned the "network speed change" thing, where it will throttle what it's sending. I blame that more on Suddenlink than I do Netflix, but I do have to question when it's playing a movie at full HD quality, then detects a change and throttles it to... full HD quality. All that does is interrupt the film. I'd much rather they made the change on the fly rather than having to rebuffer the stream, which is REALLY annoying. It's like buffering a Youtube video, it just stops in the middle of a scene, goes to a black screen while it rebuffers, then picks it up at the same point (so you usually miss a few words).
There are also instances where the stream is screwed up in some fashion. The second season of Dexter has the wrong aspect ratio throughout, obviously made by someone who didn't have a frikkin' clue what he was doing. I watched Phantoms the other day, and the sound was completely out of phase and absolutely horrible. To make it worse, there's no "suggestion" box or any place where you can address specific problems or tell them in plain English what the issue is. I filled out one of their little "questionnaires" about Phantoms, and was only able to tell them that the overall quality of the film was unacceptable, but I wasn't able to tell them why, which means they won't be able to fix it. Their customer feedback needs some serious work.
Granted, I have been able to catch up on things that I missed the first time around, like Heroes. I definitely haven't worn out the content that's available, but I'm sure I will eventually. At some point, I'll have seen all I want to see, and everything else will be "disc only", and they can kiss my ass, I'll just cancel my subscription at that point.
Overall, I'd say I'm "okay" with the service. It could definitely stand some improvement in several major areas, but that's counterbalanced by the convenience. We were discussing Bruce Lee at work the other day, and I queued up Enter the Dragon while I was at lunch (iPhone app), then watched it when I got home. That part of it can't be beaten, I just wish they had a better selection, better streaming adjustment, and better customer feedback.