i just put a disk on my road bike. i assume we're talking road bikes here in the road forum?

i took my lightest single speed with my new Shimano XT hydraulic brake (140mm Avid HS1 rotor front only) and my 160 pound body on an 8 mile trip through town, to the nearest mountain. climbed about 600 feet, descended, and rode home. the brake worked fine. i didn't do anything that i don't normally do WRT braking. no sqeaks or squeals. i suspect all the "breaking in" stuff is just a bunch hooey, dreamed up by LBS mechanics to get all the new bike owners, at least the ones with squealing brakes, with a bad case of buyer's remorse off their backs.

similar to what guitar salesmen tell new guitar owners to get them off their backs. about the time it takes a new guitar to "open up" .