Dannihilator, to the best of my knowledge, all Shimano's 10-speed mountain stuff including the 770-10 are DynaSys and are cross-compatible insofar as rear indexing goes, which is something to be thankful for... weird exceptions to the compatibility rules are always a bad thing

On the main topic, I'd take 10-speed Shimano DynaSys over 9-speed, and one reason is that DynaSys requires significantly more cable travel per shift, reducing the impact of less-than-perfect cable & housing condition. The 2x/3x mode switcher on the XT and XTR front shift pods is also nice. Another benefit of 10-speed is the 11-36 cassette option... the less chainring changing you have to do, the fewer opportunities for chainsuck, chain drop, or big changes in momentum (classic case: dumping to the granny ring on a steep climb).

Someone asked why 9sp had to supplant 8sp. The answer is MegaRange. The 11-34 is still the most popular cassette I see on customers' mountain bikes.

For those who simply oppose progress because it wasn't your idea, well... when I started mountain biking in about 1989, a 12-28 7-speed with a 26-36-46 was the de facto standard. How many of you would be happy with that today? All rightie then Save your outrage for XTR Di2 electronic shifting when it arrives; shouldn't be too much longer, I don't think.