I'm weighing this topic, and rather than start another redundant thread, I thought I'd resserect this one. I'm putting together a Surly Troll, mainly for touring, but also for occasional local riding. I've looked at mechanical discs and V brakes, and here are my thoughts, etc:

- If you'll be riding frequently or occasionally in wet conditions, discs are definitely worth considering. They work more effectively, and are likely to greatly extend rim life.

- As others have mentioned... If you will be traveling extensively in isolated areas, I would be hesitant to use disc brakes: While mechanical discs are relatively simple, they are still more complex (more parts, longer cables, etc.) than rim brakes, so if you are victimized by Murphy's law, it will be much more problematic.

- I've only ridden disc-brake bikes a few times, but in my experience, in dry conditions there's negligible performance difference; decent V-brakes work about as well.

While I haven't firmly decided on my components, right now I'm leaning towards V-brakes: I'm an ardent subscriber to the 'Keep it simple' philosophy. While mechanical discs are still relatively simple, there's still more that can be damaged/malfunction than rim brakes. With good V-brakes, about the only thing that can go wrong is cable breakage, which is very easy to fix.

I'd certainly consider discs if I were planning to tour in inclement weather, but with careful planning I hope to avoid wet conditions. I'm not so much of an zealot that I've completely ruled out discs, so if there's another good reason to go with discs, I welcome additional input.