I've used road rims for over a decade on my mtbs (both rigid, one a single speed) -- Velocity A23 (front), IRD Cadence (front), Mavic Open Pro (front and rear), Mavic Ksyrium (front), and DT Swiss TK7.1 (a "trekking" rim, rear). Only recently have I added an authentic MTB rim to my bike when I added a Lefty fork to my bike -- a Stan's Crest laced to a DT Swiss Lefty hub. None of the "road rims" ever really failed on the front, at least with respect to being knocked out of true, and they are very light. I have no issue with using road rims other than I do buy into the wider is better mantra, but even road rims are moving that way (as in the A23), so I'll continue to use them. My biggest issues have been pushing the low psi thing and dinging the rim, creating a bulge/flat spot that then interfered with rim brakes. The rear wheel is more fussy because of having more weight on it and taking more direct shots, but I've had good luck with the DT Swiss TK7.1 rim there. I've got one salted away waiting for my next build. My Ti custom frames were built for V-brakes (one is 10 years old, the other 8) and still work for me so I'll keep using the V-brake setup...