I think Gears 3 will be bumped to March 2011, that's right, I'm predicting a delay of a game that hasn't been announced yet. A delay from a release date that hasn't been set either. So technically it's not a delay, but I'm pretty sure everyone was under the impression that Gears 3 would be a fall 2010 release, before the Natal launch changed our perception of that release window.
Unless Gears has a huge Natal component that makes it a suitable launch title for the platform, I think Microsoft would be wise to keep it's two big shooters as far away from each other as possible. I mean, like someone else said, there will be a new Call of Duty in November 2010 and a new Halo probably a month(or two) before that. Halo and Gears were supposed to alternate year to year, Gears '06, Halo '07, Gear '08, Halo '09 and then Bungie change that by announcing Reach for '10.
I'm not saying two big games can't succeed together, but three big shooters that share a common fan base (well, I play all 3, so I think others do too) doesn't seem like a smart move when you're launching a new casual friendly image for your console.
Oh yeah, and they wont announce any of this any time soon. They didn't announce Gears 2 until they were nearly 6 months out from release.