I think if you are only buying a 360 for Gears of War alone, then it's not worth it, but then again, it's (relatively) cheap, so it can't hurt. But if there are other exclusively-Xbox gaming franchises that interest you, then buying a 360 is a no-brainer.
The bottom line is: focus on games, not tech-specs. That's the reason I'm in no hurry to get a PS3, yet.