Another vote for the Maxxis Desert IT for longevity. I don't use it as a race tire by any means, but for trail riding 2-3 times a week in the rockies of colorado (lots of pointy, sharp, tire eating rocks), its hard to beat. It definitely starts loosing traction when worn, but I'll take loss of traction over shelling out money for a new tire every few weeks.
Maxis IT... however, it SUCKS in the Pacific North West!
so no good for roots/rocks/loose/wet/mud?
It will probably work better with a Tubliss.