I've toured for hundreds of KMs of muddy roads with BB7s and the caliper/disc rotor is quickly contaminated with mud [if its runny] which affects the braking performance. I think where a disc brake would be best would be in sticky mud where it's more likely to stay on the tire and where it would clog up a rim brake. I haven't toured under those conditions yet and have only mountain biked in that sort of mud a couple times. Depending where you live it might be a more common occurrence.



I haven't had any issues stopping my v-brake touring bikes in the rain/mud nor had any rims wear out uber fast or blown any tubes from overheating when braking.

To be honest I would like to tell you disc brakes are the silver bullet to all cycling braking needs - especially mech discs because they are easier for most folks to work on at home and easier repair in the field, but so far that just hasn't been my experience.