Why bother? The 10 speed chain is narrower and weaker. I would have gone 8 speed on my 29er if i could have, but there isn't that much quality 8 speed stuff out there for mtb. My friend tries to ride trails on his CX bike, but you put a LOT more torque on a mtb chain than you do on a road chain (big fat tires plus steep climbs). yes, if you spin you will be fine. but for the average mountain biker, who will attempt to mash in a cross chain situation, have fun. im sticking 9 speed until the bitter end. and even then, unless my road bikes are 10 speed (currently 6,7, and SS 1/8 inch drive), i will stick with 9 speed.

I think that 10 speed is ridiculous on a mtb, and the average user will end up suffering. this is just opinion, but when i told my LBS that sram x7 will be 10 speed, he said "oh god". this is a man who still rides 9 speed ultegra.