I've had my MT/R's for about 6 months now. They ar a SUPER tire, not only on the trail but for driving in general.
They seem to be holding up well, a little bit behind my old Scorpions AT's, but very still very well for a tire with such a soft compound.
On the trail, I feel that you were wirth the $$$. Excellent grip when aired down and surefooted lateral traction. Sidewalls are firstrate, very tough and forgiving. Unsurpassed on rocks.
Downside, others have stated that if not properly rotated, they wear unusually fast. Also, some feel as though the cost is too high, obviously.
Overall worth it if you got the money.