I find the Netflix interface really poor actually. I wonder how bad the others must be for this to be better.
Unless you know exactly what you want, it's difficult to find a movie. There's also no way to bookmark or wishlist a title so if you find something you do want to watch, you have to watch it right then. Going back means you have to remember which titles you liked and then remember under which genre you found them. The iTunes interface is actually much better. You can search through popular titles, you can browse by actors/producers/directors and the wishlist feature is very useful.
I've been using Netflix for a week and now see why this is no threat to iTunes. 9 out of 10 tv shows or movies that I look for come up unavailable.
It's not bad for documentaries or killing time with one of the older movies. If you have something in mind though, the odds are you won't find it on Netflix.
For $7.99 per month, I guess it serves its purpose nonetheless.