I got a set of nobby nics a few weeks ago. I'm running a 2.4 up front and a 2.25 in the back. Let me just say, this things are pretty much the *****. I had motoraptors on before, I lost a pound off my bike with the schwalbes. They're great for the nc singletrack, with loose crap and pine needles over hardpack. They hold on like crazy, but the thing I love the most about them is that they break away so predictably, you can correct before they fully lose traction.
I'm running really low pressures in these tires, 25 up front and 32ish in the back. The back will squirm if I take it down to 28-30. I haven't pinch flatted yet, knock on wood.
cons: these tires are hella expensive. I work at a bike shop so I get parts at cost, but cost for these tires is more than some tire's MSRP. Thats no good. also, they seem to be wearing fast, which is not surprising given that they are as sticky as they are. When the back wears out, I'll probably replace it with a hutchinson spider, but I'll keep buying the 2.4'' nobby nic for the front.
anyways, thats my little review. hope you folks liked it.