http://xbox360.ign.com/articles/919/919647p1.html
A Konami rep is quoted as saying, regarding MGS4, "We're actively looking into a release for the Xbox 360." While this isn't a confirmation of it coming, it does lend hope to those Xbox 360 owners who haven't plunked down money on a PS3.
However, this little quote doesn't clear the major hurdle Metal Gear creator Hideo Kojima has listed for the title coming to Xbox 360. He has been quoted in several interviews saying a port was likely impossible due to the game being optimized for the PS3 hardware, specifically Blu-ray discs.
Let the "discussion" commence!