Here's my Monster-X coming from the other direction. It's a stock Trek 520 touring bike with the fattest tires I could stuff into the fork.
I've posted the images before, so I'll take a moment to review the tires. These are Ritchey SpeedMax (iirc) 700x40c tires on the fat touring rims the bike came with.
They are incredibly quiet and smooth on pavement. I notice the extra weight a bit vs. road tires, and the top speed is somewhat slower. The edge knobs don't inspire the same confidence in turns that my road tires do, so I tend to turn more deliberately when leaning the bike.
These have been very tough on the trails so far. The first time out I tried airing them down too much and, after snakebiting a couple tubes, road 3 miles back w/o any air in the rear. The tire didn't look worn at all and has held up since. I've had them on some quite rocky and occasionally sharp trails, and they don't show any significant wear yet.
Some rocks (but smooth ones here):
There are limits to the dirt traction, but they are surprisingly high, even with 65lbs of pressure. I've only been in hardpack, some loose over hardpack, gravel and some rocky bits; I can't comment on the wet/mud aspects of the tire, though.
All in all, I've been surprised with their capability on both trail and road.