Yeah, I agree with all of the above. Rollers mimic real riding better than a trainer so you develop balance and a smooth spin, but standing is bad and don't let your mind wander! Keep the rollers close to a wall so you have something sturdy to grab - perhaps between a wall and your bed but not a glass anything.
Go over to bikejournal.com and seach/ask your question also. Several of the folks over there use rollers.

I also use a Cycle-Ops trainers and Spinervals. I can stand up, do one-legged drills and vary gears which have all helped increase my power output as opposed to just spinning along. The DVDs give me a focused and structured workout, which I am too lazy to develop on my own, and can be far higher intensity than the same time out on the road.

I also read somewhere that the new DVDs allow you to turn off the music. Whew!