There is a good article on FastCoLabs: What’s The Big Problem With Developing Oculus Rift VR?
It seems it is not that hard to integrate into a game. Team Fortress 2 has an Oculus Rift interface now. Valve, the owners and operators of Steam, helped create the interface.
Joe Ludwig, one of the Valve programmers behind the Rift implementation, said, “Figuring out how to combine mouse and keyboard input with head tracking was not very well explored territory, so we had to break some new ground there.”

