Fwiw, after the fact, I ride both mtn and road. I love my hydro discs on my mtn bike, I wouldn't ride in the dirt with anything else.

Having said that, I have Sram Force rim brakes on my roadie, and they stop me so well, I think discs on a road bike are a solution looking for a problem.

If I were running carbon wheels and tubulars, I may think differently, but I'm on alloys and clinchers, so they're perfectly fine (and a poundish lighter).