I have seen 3 instances where a bent rim could not be straightened. One was a steel rim. Two were heat-treated TREK MATRIX TITAN rims, from a 1985 trek 500. In the two latter cases, I went down a pothole with the MATRIX TITANS, causing them to bend, and the heat-treating made the rims so rigid and strong that the LBS could not get them true again (I'm no lightweight at about 210 lbs when this happened.)
So personally I prefer soft, compliant rims, like the original weinmann 210/256 rims, because they can be straightened, and they can be trued.
I have a set of concave rims, but have only ridden them about 10 times, and have not had problems with them. they came on a bike - a well-worn raleigh pro - that had been "all over the UK" and the rims were an obvious retrofit, and are the earlier, eyeletted type, so the rumors of durability ring true to me ...
- Don Gillies
San Diego, CA