Convenience is the main factor for many Netflix members, I suspect. I used to have a Netflix account. I liked the fact that the dvds showed up in my mailbox and had postage paid returns. I go to my mailbox everyday anyway, so the added effort was minimal. Lack of late fees was great too. The other main advantage was the queue. I just selected a slew of movies that interested me and sat back as they came to me, a few at a time. I didn't have to remember a list on my way to the video store, or wade through what was available at any given time.
Even when I had a membership though, I started to become annoyed by the fact that they wouldn't ship out on a Saturday, which limited the number of movies I could get per week, even if I were disciplined about watching and returning my movies quickly.
When frugality became a part of my life, I cut back on the number of rentals from Netflix at a given time, to save a little money. Pretty quickly though, I put my account on indefinite hold and started getting my movies from the library for free. With each movie I got from the library, my Netflix queue shrank. It's true that every once in a while I get hit with a late fee, which racks up at the rate of $1 per day for dvds. (Late fees on books are much cheaper.) But so far, I've paid about $3 in late fees in almost a year of borrowing dvds, and I'm happy for the local library to get a little cash out of me.
Two other things make getting dvds out of the library the way to go, in my opinion. Firstly, my library allows patrons to keep a list of books, cds, and dvds on their server that can be accessed either from home or while at the library. This pretty much replaces the Netflix queue. Secondly, whatever dvds are not in my library's collection can be requested through inter-library loan. So far I've only struck out completely on one dvd. That's a pretty good success rate, I think. And it's all free if I'm reasonably organized.
Once again, the two virtues of patience and planning in advance make the virtue of frugality no hardship at all.