My dollars voted for the OM-D around Thanksgiving time, and I voted the same way in this poll.
I have been a Nikon customer since 1981 and currently have a D700 and lenses ranging from 14mm to 840mm (with stacked teleconverters). The D600/D800 don't bring anything new to the table that I don't already get from the D700. Nikon FX gear is neither small nor light and air travel with FX gear involves a real commitment. I have been wanting a more portable solution for a couple of years. I have been hoping Nikon would make a serious entry in the mirrorless market but I finally gave up waiting for them. The OM-D (along with 12-50, 35-100 and 7-14 lenses) seems to be a fairly competent photographic tool in a nicely sized package and checks off most of the boxes on my list of requirements.