The independently owned company have long maintained a strong partnership with Sony, but once again industry bumblings and anonymity are hinting that Insomniac will go multiplatform.
Sony own both the Ratchet & Clank and Resistance franchises, so if you're expecting those on XBOX 360, well, think again. In all likelihood, if Insomniac do release something on XBOX 360 it's likely to be a smaller XBLA title. It's also extremely unlikely that any future Insomniac game will not hit the Playstation 3 in the future - given the long history between the company and Sony.
Good news you should assume from this: Insomniac are making games.