I've been impressed with the ones on my old bomber mountain bike. An aggressive 200 lb. riding partner borrowed them for a trip to Moab last summer and couldn't hurt them. They were fresh out of my truing stand and had never been ridden at the time. After a hellaciously long 40+ mile day up Kane Creek Road out to Chicken Corners and back in 95ºF weather the rear wheel was only about 0.5mm further out of true than at the beginning. They've since been used for a number of 2 ft. drops off the ramp in the backyard and stayed true after having been brought back in.
That said, it's the build more than the rim. I've had some pretty cheap rims take an awful lot of abuse given optimal spoke tension.