There has been some rumours about a Kinect-based Gears of War-game for a while, and now Kotaku say that they've talked to "sources claiming to be familiar with the project" that say it is real. There is supposedly a demo, which uses events and assets from Gears of War 2, and the whole thing is supposed to be an on-rails shooter.
The picture below, published by Kotaku, is said to be from an early version of the game and it "may not accurately represent the final product." It looks rather dodgy in general, though...