I've been pleasantly surprised by my recently arrived Rift, and believed my first adaptation problems to be because of a lack of VR legs, but somehow I felt there was something wrong. I've been feeling some sort of stuttering/lag when moving my head around, even with really slow movement, as if the image "jumps" frames unevenly. This also translates to increased perceived motion blur and lag when looking around. It feels very unnatural and is really disorienting. This happens with every single demo/game I've tried (Unity/UDK/HL2, even those that run at 60 fps) and it's progressively making me more sick each time I try, as I'm now more aware of this. My brain struggles trying to compensate for the stuttering/lag, and it not only causes motion sickness but also eye strain. About an hour ago I downloaded the Vireio drivers and tried Dear Esther with them (mouse emulation)... the head movement is WAY smoother, no stuttering at all, and the perceived blur is greatly reduced. It feels much better than anything else I've tried (the caves are amazing). I don't have any other gaming PC to try the Rift on. I'm on a fresh Windows XP install about a week old (correctly updated) so there's not really much that could possibly be conflicting, but who knows (no Logitech software here)...
Another problem I have is that I can't run the Oculus SDK IPD Utility, it tells me that I'm missing dxgi.dll (which seems to belong to DX10 and higher). Is the utility not compatible with DX9? The same happens with the Oculus World and Tiny Room demos.