How easy are Parabolic v. Standard Rollers to use?
I've never ridden parabolic rollers myself but I do have a pair of cylindrical pvc rollers. It takes a bit of practice, but after a short amount of time I was able to watch tv quite easily from my cylindrical rollers. A bit after that, I was able to sit up, lean back down, take a drink, and ride with one hand or one foot while watching tv. Not all at the same time, obviously.

It is my understanding that parabolic rollers are easier to learn to ride simply because you can't ride off the edges. However, riding off the sides isn't a big deal. The bike comes to an immediate stop. The friction of your tires isn't enough to overcome your body's lack of inertia. You smell burnt rubber and may leave burn marks on your carpet, but that's about it. If you put a towel under the rollers, you won't have to worry about the carpet.

One other thing to consider is the diameter of the riding surface of the rollers. I believe that on average parabolic rollers are smaller than cylindrical rollers. Smaller rollers heat up more quickly and as a result are harder on tires. 

I've really only addressed the issues between parabolic and cylindrical rollers here because that seems to be the brunt of your question. For a more comprehensive disucssion of rollers, see this question and the questions that are linked to in the accepted answer on that question.