I'm consider getting bicycle rollers for use over winter, and I expect after the initial newness has worn off it might become boring. Can I realistically watch a DVD while using rollers? Or do they take too much concentration, and I should look at getting something like a fluid trainer instead?
Rollers are awesome! At least I think so. I have used both a trainer and rollers and I much prefer using the rollers. Once you are used to using the rollers you will be more than capable of doing things like watching a movie.
One of the best things about rollers is they magnify issues with your cycling form. Once you have trained enough on the rollers your body will figure it out and it will start to be second nature. It's fairly entertaining to do a youtube search for bicycle roller tricks. I don't suggest doing any of those tricks but worth a few minutes to watch and laugh.
There are several different kinds of rollers, so I would suggest learning about some of the pros and cons of each discussed a bit in another question => http://bicycles.stackexchange.com/questions/1663/should-i-buy-a-pvc-or-aluminum-roller
I agree with Mike - the first time I come off the rollers and hit the road I can definitely fell the difference in my form, particularly with my cadence. They're great as an adjunct to regular season cycling, too, since they really force you to concentrate on a smooth pedal form (if you're "pushing" the pedals as opposed to turning them you'll surge back and forth).
I'd recommend starting up next to a wall or in a doorframe since it'll take a little while to get used to balancing on them and staying in line on the rollers. Don't give up - we've all fallen off them.
And definitely check out the range of rollers available; I have some nice Action Mag aluminum smooth rollers with an adjustable flywheel on them, but you can do what you need to do without a lot of the add-ons (and add them on later, too)
As far as getting boring, I usually listen to music, either on an iPad strapped to my arm (so I can flip through my play list) or on the stereo. If you're just starting out I'd suggest avoiding watching TV and concentrate on a spot about two feet in front of your front wheel. Sounds weird, but it helps keep you straight.
Getting used to rollers is similar in difficulty to driving a manual transmission car. The first day will be really tricky (especially the first hilarious 20 minutes). Soon, you get familiar with it enough that you can use the rollers without needing to occasionally grab something for stabilization as long as you have total concentration. Over time you develop motor skills that kick-in and that frees up your concentration so you can do things like sip water or watch TV or juggle.
The main point is that the amount of actual concentration that you need will decrease as your motor skills develop. Eventually, you won't need to "think" about it when on the rollers at all. The amount of time this takes seems to vary a lot and depends on how much practice you're willing to put in.
The purpose of rollers is different from trainers. On rollers you're developing form. This translates to increased efficiency on the road. The trainer is more about developing strength and power.