I run the Rocket Ron as the rear tire on my Santa Cruz 5010 for riding on the mostly-dirt trails around Park City. First and foremost, they have incredible traction. I previously rode Saguaros on a 29" bike, and there was a marked improvement, especially on slightly loose, steep switchbacks.
The drawback is that I only made it through half the summer before needing a new tire. Some of the knobs had broken off, and I found I was getting a fair number of flats.
But when it came time to get a new rear tire, I still went back to the Rocket Ron 'cause the grip was so good!