While rollers won't give you the same level of workout that a trainer will, they are far more enjoyable and require your complete concentration (no watching TV unless you have some damn fine skillz). Once you get the hang of it, you will notice you are able to hold a much straighter line and ride with more confidence when you get back out on the road.

If you are still can't decide between rollers and a trainer, remember, Eddy Merckx used rollers. That is enough for me.