Shimano Deore XT 10 Speed Dyna-Sys Drivetrain M780
Coming back with a vengeance for 2012, the Shimano 10 Speed XT Groupset continues to be "the standard" for serious mountain bikers all around the globe. The big news for this season however, is that Shimano have increased the available options with your choice of a double or triple chainring setup, as well as XTR-inspired styling of the derailleurs, shifters, chain and cassette. Far from just adding on an extra cog to the cassette, the DynaSys ethos focuses on improvements on every component in the Shimano XT drivetrain that add up to give you faster shifting, higher efficiency and improved durability over the previous 9 speed system. While you might not get the same shiny Titanium or Carbon that you get with blingy XTR, the Shimano XT drivetrain gets you XTR performance at an incredible pricepoint.

From Shimano:

"Shimano has been making mountain bike drivetrains for more than three decades, including eight generations of Shimano Deore XT (the original MTB drivetrain) and six generations of its flagship XTR group. Each generation is a reflection of the riding that defined the sport and the technology that defined the era. True to this legacy, our next-generation Dyna-Sys drivetrain brings with it the legendary quality, durability and performance riders expect from Shimano, all packaged to meet the ever-evolving demands of today’s riders".

So what exactly have they improved on?
Well aside from the obvious inclusion of a 10 speed cassette, Shimano have made several key changes to imrpove shifting on your bike. The XT Chain itself is now a asymmetric number, with one side that is made to work optimally with the shifting pins and ramps on the front cranks as you move into a bigger chainring, and the other side is made to work with the shifting ramps as it climbs up the cassette. This is particularly noticeable when shifting under load, as the 10 speed drivetrain is so much quicker and more accurate than previous generations.
The XT Cassette has a larger spread of gears than the old M770 version, with an 11-36t option giving you a super low gear for technical climbing and being particularly popular with bigger-wheeled 29er bikes. They still have an 11-34t option which will be better for XC riders, and both cassettes feature ratios that are tighter due to the extra cog.
Due to the change in ratios at the back, the XT Crankset received an adjustment to the teeth ratios to make front shifting even better. Instead of the old 44/32/22 chainring spread, the new cranks use a 42/32/24 spread to reduce the gap between each shift. On the new 10 speed drivetrain, the lowest and highest gears are almost identical to the 9 speed setup, though there are now simply more usable gears in between those extremes.

And what does this mean out on the trail?
Well the main benefit is that you'll reduce the amount of shifting up front, which most people will agree is a very good thing. With a bigger spread of gears at the back, you can spend more time using a single chainring with less need to shift around up front, leaving you to spend more time focussing on the trail ahead. This is also advantageous on a dual suspension bike, as most duallies have their rear suspension designed to work optimally around a 32t middle chainring - if you spend more time in the middle ring, you'll have less suspension feedback and less suspension bob. With the XT cassette available in both an 11-34t and an 11-36t, we would recommend the smaller ratio for 26" bikes and the larger block cassette for 29er riders that need lower relative gearing to smaller wheeled bikes. 
After spending some time on the new XT Groupset, we can honestly say that it is smoother and more responsive than any 9 speed components from the past - which is exactly what you want from your drivetrain.

The Shimano Deore XT M780 Groupset includes:

• Shimano XT Crankset: M780 with 24/32/42 triple chainring (165, 170, 175, 180mm lengths)
• Includes XT Bottom Bracket
• Shimano XT Shifters; Choice of standard bar clamps or integrated I-Spec Mount (for use with M780 brake levers)
• Front XT Derailleur (Hi Clamp, Low Clamp, E-Type or Direct Mount - check your bikes specifications) 
• Rear XT Derailleur; Long cage for 3x10 setups
• Shimano XT 10 speed Chain
• Shimano XT 10 speed Cassette (11-34t or 11-36t ratios available)

The 2012 Shimano Deore XT Groupset provides XTR level technology at a trail-ready pricepoint