I have disc brakes on some of my bikes, cantis on some and road bike calipers on a couple. I don't really think any of these systems is perfect for every application. My touring bikes have v-brakes and I have no issues with stopping power rain or shine. I don't overheat my rims in the mtns.

I use v-brakes because:
- allows you to use a fork with vertical compliance to absorb road vibration
- inexpensive $25 a pair
- lots of stopping power
- modulate well
- easy to adjust
- easy to get parts for
- light
- simple
- easy to repair
- doesn't require dish in front wheel and less dish on rear than disc
- not easily damaged during transport

Disc brakes do have some advantages:
- better in all weather, especially winter & mud
- better for really heavy loads as you can get bigger discs [however - you need an appropriately strong fork/frame or all you do is damage your bike under severe braking]

However, there is no magic bullet and unless you are riding an Xtracycle hauling a ton or winter commuting or off road touring down muddy tracks I don't think they add much value to your bike while making it much less likely to be repairable internationally.

One often quoted reason to get discs is to avoid over heating rims. First off read this article and appreciate your discs only have a finite heat capacity before they are damaged. Second consider that you may be using your brakes poorly. Applying the brakes constantly for a long duration is a recipe for disaster. Shorter stronger applications allow your discs and rims to cool down in the air flow. You can validate this yourself. Go down the same long hill twice apply your brakes lightly, but consistently the whole way down to keep a constant speed. Then try the same hill again and keep the same approximate speed by applying your brakes strongly and then letting them off for a bit - repeat. Check the rims at the bottom - which are warmer.

Quote from the article I linked to above - it talks about tandems, but a heavily loaded touring bike has the same issues:

"Tandemists who are using the current crop of mountain bike disc brakes on their tandem should keep in mind that none of the current disc brakes are designed for tandem use. All of the current disc rotors are too small and light for tandem loads on big hills with heavy teams. Some of the rotors are too light even for light teams on medium hills. In the right conditions, the rotor will overheat too quickly because of its low mass (and therefore low capacity to absorb braking heat).

Certain people are successfully using existing single-bike disc brakes on tandems, without risk of brake failure. Those people ride in flat places with no big hills. The next question those people may wish to ask themselves is why they have bothered with the expense, complexity and extra weight of disc brakes when rim brakes would have offered perfectly adequate performance.

Rim brakes on a 700c or 26" wheel have a mechanical advantage over a typical 8" disc brake because the radius of the braking surface is much smaller on a disc rotor than on the wheel rim. Much more braking power can be applied with the rim brake (about 10 times more, thanks to the miracle of leverage)."

I'm not suggesting disc brakes are bad or they should not be used. However, there seems to be a very simplistic view of how brakes perform that suggests discs are better than a canti brake without factual basis for this argument.