My main experience demoing the dk2 around was that the first thing everyone did was try raising their hands in front of their face, and that motion sickness hit about 30% of people. The Vive fixes both of those problems, and they're first to market.
Still, facebook has deep pockets, and from everything I've heard their headset is better and their controllers are better. I can't wait to give them a try.
The next big thing that I want in VR is multiplayer.