I actually do own a Minoura rim-drive (magnetic resistance) trainer. I'm not exactly sure it's the same model as the one you tried out, but I'll give you $.02, for what they're worth.
I like it. I can throw either of my bikes on it, which have different rims and tires and have no adjustments to make, as far as wheel contact goes. The rim contacts are essentially "rollerblade" wheels, spring loaded against the rim, which can be locked out of the way while loading and unloading your bike. One of the drive wheels is attached via belt to what is basically a small generator (don't think <i>that</i> hasn't gotten my EE mind running on how to tinker with it and for what purpose to usurp it). Contrary to some comments I've heard, it doesn't get easier to pedal the faster you go, as each pole of the resistance windings pulls back fairly consistantly. Obviously, I haven't whipped out a force gauge to actually test this, but going by feel during workouts, that is what I've noticed. You also can't build up much momentum, as, whenever you stop pedaling, regardless of pace, your rear wheel will stop spinning in one to two rotations.
As far as wear on the rim, because the drive wheels are pretty low durometer rubber, the odds of damage to a standard aluminum rim are pretty much nil. You can get the wheels to slip occasionally, however, during start-up and if you break too hard, which might concern me if I ever used it with carbon wheels. Honestly, the occasional spin out of the blocks, though, is hardly a concern considering what effect breaks have on wheels — you adjust the drive wheels to work on the breaking surface of your bike's wheels. The one exception I will add here is that if you have a painted rear wheel, you will wear off your paint more rapidly than breaking alone would. This, of course, depends on how the wheel is painted and with what paint, but with more constant contact than occurs during breaking, the paint can be worn through fairly quickly, again, with no damage to the underlying metal. I doubt the same effect would occur with color-anodized wheels, but have not tried them out to date.