Information recently gathered about the highly anticipated Gears of War suggest that a demo should be coming to Xbox Live very soon.
Microsoft recently showcased the title at an event they held a few days ago, and Xbox.com PR person John Porcaro has written on his blog that the game is now playable in some form (for the first time), and it looks amazing. He can be quoted as saying - “holy smokes” (no real surprise about his enthusiasm there).
Porcaro has further said that it might be the game of E3, when it could be fully playable for the first time. If it is playable, then we can expect a hands on with the game come May.
So while the demo may not be imminent on Live, you can rest reasonably assured that it will be there soon.