It can be. I had netflix for a long time and there's nothing like being able to watch anything you want without ever having to get up and leave the comfort of your home. Plus, the programs are relatively inexpensive.
The original incentive of getting X number of DVDs for $1 can be very enticing. Though you have to realize that to do that, you have to buy 12 at the normal cost. So if you can afford that in the long run, go ahead.
A dvd club is a good idea if you are looking for older movies at a good price. They are easy to find but I think a rental club is more cost effective today.