There's still a lot of work to do to get the rift running smoothly, specifically I can't seem to get the thing to focus properly in fullscreen mode (but works great in windowed!).
I found the SDK alright, but a little basic. The examples and API itself use a RH (right handed) coordinate system, which is not what DirectX uses, and I wish they supported both out-of-the-box instead of me having to map between them. "Oh here's a quaternion providing the headset rotation, but it needs its coordinate system remapped"..uh-huh. Oh yeah, some documentation on using the rift with DirectX would be nice!! OR am I the only one using DirectX these days?
In order to render for the rift, you need to draw your scene twice, with the camera offset by the distance between your eyes. It's nice and easy, as the geometry of the rift lenses is such that you don't need to skew or rotate your projection matrices, it's just a translation. However, drawing the scene twice obviously incurs a performance hit if you're not careful. Thankfully the Stingray Engine I built for Pegwars builds up command buffers for drawing, meaning you can re-render just the scene's draw commands from two perspectives - without duplicating any setup work. Nice! My only problem right now is I'm creating light-maps twice, which obviously can be reduced down to just once per frame. But overall, I was very happy with the rift rendering performance... certainly much faster than 50% of the single-view frame-rate!