Lindsay got me thinking about Netflix. For $18/mo, you can have 3 DVDs at a time out, and can return them any time for more.
The feature that got me was your movie queue. I had disregarded services like Netflix before because I didn't like the hassle of having to select a new movie when I sent some back. With the queue, any time you have an idea you can add it to your queue, and it will just show up! Of course, I probably shouldn't mention the archival potential, but I just did ;-).
The biggest thing I'd be worried about is not getting my money's worth; although two DVDs at blockbuster will cost you about $8, and if they're new releases, you had better have them back in 2 days. So, for the cost of 4 Blockbuster DVDs, you get as many DVDs as you can swap.
What would be killer is if I could add movies just coming to theaters to my queue; because commonly I see a trailer for some move I want to see (say, The Incredibles) but don't want to go to the theater to see it. I wouldn't mind it just showing up in my mailbox 7 months later.