@Bas: We user tested push to select and it didn't seem to work well at all. Of course, at that time I was using the OpenNI SDK,so I'm not sure if the unreliability was attributed to that. My guess is not. We found that the "push" gesture opened up a lot of variability. Some envisioned a push as simply tapping their fingers forward...others exaggerated their entire hand forward. Ultimately, you can't support both instances because that will just get confusing (might complicating other scenarios in which subtle gestures might come about). Not requiring a push removes consideration of the z-axis with restricts the space of actions down to something more reasonable (2D in a 3D world). It's also no surprise that the Xbox team and most games limit it to a "hold to select".
I've heard muliple sources say that push to select doesn't work. I guess it's just one of those things that seem obvious but just don't work in practice. I guess hold to select is acceptable (at least it works) but I'm still waiting for someone to come up with something less awkward. Personally I think there's potential in Kinect's voice recognition abilities. Although it certainly doesn't help that it's limited to only a handful of regions.
Regarding the pelvic thrusting: ever since the SDK came out I've been wanting to create an application that uses depth maps to detect... swellings, and then tilt the camera downwards in shame. I was going to call it Kirect.