Not only have SRAM won the race to bring the 11-speed drive train to mountain biking, they have pushed the less-is-more envelope further to introduce 1x11 speed at XX level for 2011. Personally, I think it should have been called XI (11 in Roman numerals, like XX is 20) but that is just semantics – they have dubbed it XX1.
So there is just one dinner-plate sized 10-42 cassette in the group, and half a dozen optional chainrings, all fitting the same spider. Since the derailleur doesn't have to wrap up as much chain, it has been totally revamped and is more precise and sturdy. To avoid the need for a chain guide, the chain ring and jockey wheels have teeth machined to perfectly match the chain's alternating plates. The chain is slotted and since there is only 1 cog up front, it doesn't need to flex as much so is very strong.
Having no front shifter or derailleur and one less chain ring makes for serious weight savings and virtually eliminate any chance of missed shifts, but this is no news to the many people who are already running 1x10. The 11 speeds effectively add another gear, so mitigate the compromises somewhat.
Shifters come in either trigger or twist options. Of course being the top group, the cranks are carbon.
A 2x10 drive train has a development ratio (percent difference between highest and lowest gear) of 490%, whereas the 1x11 is 420%. The intention is the front cog is chosen to suit the event or local terrain. Front cogs range in size from 28 to 38 teeth in 2 tooth steps. So if you're doing Karapoti, run the 28T front, or Santoft maybe something a bit bigger.
Nothing has been said, but 1x11 is sure to filter down to the lower groups over the next couple of seasons.
You can read all about it and watch a video of the development team explaining the process at http://www.sram.com/sram/mountain/family/xx1. The groupset is due for global release in October but the laws of supply and demand will ensure it is hard to get and carry a price tag to match. The best option is to look at new season's bikes with the group set as standard, hundreds or even thousands can be saved this way thanks to the buying power of the major bike brands.