http://connectedconsoles.com/ps3-Kojima-to-return-to-PS3-thanks-to-Modern-Warfare-2.cfm
Modern Warfare 2 has inspired Kojima
Hideo Kojima is probably the most legendary game developer in the business. Creating the Metal Gear Solid series, he's been a fan of the PlayStation brand for a long time. The sequel to Guns of the Patriots moving to multiplatform, though Kojima himself isn't working on it, he's currently working on the 'true sequel', Peace Walker for the PSP.
Modern Warfare 2 was released in November and according to Official PlayStation Magazine (Issue 040, January 2010), it's inspired Kojima to move back to developing for the PlayStation 3. Unfortunately there aren't any quotes, other than "After seeing Modern Warfare 2, I feel like I want to use all the modern specs!" And when asked why he moved to the PSP in the first place? "I wanted some young people to play MGS too" he said. "In Japan especially, the most popular hardware with this audience was the PSP"
Kojima is currently working towards a May release for Metal Gear Solid Peace Walker, but a younger team are currently working on Metal Gear Solid: Rising, which we hope will be released some time this year.