I'm with Frob. I was so excited when receiving my dk2 and so disappointed about the getting sick issues. The thought of running or racing around in VR is far from the execution with a dk2. I personally doubt that the prod / commercial version beginning of 2016 will solve this (with just higher resolution and fps).
To be honest, the thing is just lying around for a short test run about once a week, so maybe I'll get used to it. For me that's also the reason I didn't dig into the API yet.
In my experience (especially with the DK2 over the DK1) sickness issues is more the fault of the game then the technology itself. The DK2 has a fast enough refresh rate and good enough tracking to kind of get most people used to it. If the game is your typical "30fps is fine" explosion fest, however, it's vomit city. You absolutely need 75-90fps or more, and most game devs these days have no interest in degrading their game to meet said framerate.
There are also other things the game designer can do to mitigate the issues. For example, putting a cockpit around the player (or another stable frame of reference that is almost always in view) does wonders for preventing motion sickness, as does having a virtual body in a similar pose as the player's.
Even with all that help, though, some people just will get sick over it. I personally can't play on my DK2 as long as I play on a monitor because after a couple of hours I'll start feeling a little green myself, and I consider myself able to handle it better then several people I've showed it to. For some people, it just takes time to get acclimated, so you take it slow.
The question really becomes - will there be that killer app/game that will motivate people to do it anyway?