I don't have Netflix but I DO have Blockbuster.com. It's very similar. I'm on a 3-at-a-time unlimited plan and I pay $17.99/month. The awesome thing about blockbuster.com is that once I get a movie and watch it I can either drop it in the mail or take it to a local blockbuster and exchange it for a free movie rental. That way there's no downtime where I'm without a movie.
I have a feeling that the mailing turnaround time for blockbuster.com is a bit slower than netflix. My friends that do netflix have recieved movies as fast as 3 days after they sent in their watched movies. The fastest mail turnaround time for me has been 5 days.