Not to mention better looking and mmm, lots of carbon.You guys realize all/most of this discussion is moot right? New 10 speed MTB offerings from Sram and Shimano are exclusively offered in mid & long cage lengths. 9 speed versions of Saint, XT, SLX, X.9, & X.0 will continue forward for DH/FR/AM applications as well as for those who might be unready or unwilling to jump to 10 speed.
Having personally ridden the XX stuff quite a bit, I will say that for XC/trail/AM the 11-36t cassette paired with a 2-ring crank really is an enlightening experience. You will question the existence of 3x9 completely after you put a couple good days in on 2x10. Lighter, faster shifting, less dropped chains, more ground clearance.
-ska todd