I use an Avid BB7 mechanical disc on the front, but also leave a Deore v-brake attached so if something were to go wrong with the disc (which is unlikely given the quality of the Avids) then I still have two brakes. The Deore costs and weighs so little I figured I may as well have it there.
I wouldn't use a hydraulic disc for touring.
The only real issue to overcome with mechanical discs is that it can be difficult finding a lowrider type rack that fits round them. Not a problem for me because I use an OMM Sherpa on the front.