I've had Netflix for a couple of months now and, in fact, I'm watching a movie with the 'Watch Instantly' feature right now. It's by far my favorite feature of Netflix, but certainly not the only one. There are thousands of movies you can watch instantly on either PC or Mac, as long as you have IE or Firefox.
Here's a description of the 'Watch Instantly' feature straight from the Netflix site-
With your Netflix membership you can watch movies and TV episodes instantly on any Windows XP or Vista PC that has a broadband internet connection, or via any Netflix ready device.
Movies available to watch instantly appear on the Netflix web site with a "Play" button and an "Add to instant" Queue button.
On compatible PCs, the first time you click Play, you'll be asked to to download and install the free Netflix Movie Viewer software; after that, playback will start quickly - usually in 30 seconds or less.
Netflix ready devices can play any title that you choose to add to your instant Queue.
Just recently, they made the viewer available for both Firefox on both PC & Mac, and also- playback has never taken more than a few seconds to start. Besides that, it's been a great experience.
Not all of the titles on the 'Watch Instantly' feature are recent, so if you're interested in actually receiving recent DVDs, they do that as well. They'll ship them and they get to you in about one or two days once you have them queued up.
Personally, I like being able to watch movies whenever I want as much as I want. Plus, when you watch movies on Netflix, they're usually widescreen and you can fast forward with a preview.
Right now, they're offering a free 2-week (14 day) trial. That's more than enough time to figure out whether you like it as well. I highly recommend it.