I just made the switch. I've just ordered a disc brake road bike and am selling off my rim brake wheels (have a 80mm CC for sale still). After spending most of the winter riding my disc brake CX on the road, plus wanting an excuse to get a different road bike, I decided to make the switch. Personally, it's not the tire clearance or the all-out braking power, but the consistent feel when you're scrubbing speed or slowing. There's no grab and modulate that typically seems to come with carbon rims. Plus I found myself using the training wheels less because I didn't feel like swapping brake pads. With disc wheels swaps between race and training rims should be a lot simpler.