My Pirelli Scorpion XC didn't last very long -> 900 miles and the center nobbies were gone. It did hold up pretty well though without much chunking on the side knobbies.
I mounted a Michelin AC10 (DOT legal) on the rear this spring and ran it in Utah for the week. I loved the traction in that environment, but like the Pirelli it wore pretty fast. I rode close to 450 miles of mostly dirt that week and it's looking about 1/2 way gone (it was brand new when I started the week). As a comparison, Farnham's Maxxis intermediate desert tire was also brand new, and his looked just lightly worn when I left. But it's not DOT legal....
The next rear tire I'm going to try is the Kenda K760. Pretty good reviews, and a good price. DOT legal as well.
1976 FJ40 - green and mostly stock
1996 FZJ80 - not so stock