Overall, though, it's difficult to shake the feeling that the EOS 6D simply lacks the 'wow' factor of its main rival. Whereas Nikon seems to have taken the approach of taking away as little as possible from D800 when creating the D600, Canon appears almost to have gone the other way, removing as much as it thinks it can get away with at the price. The result is the kind of conservative, slightly unimaginative design that's become the company's hallmark. It's still bound to be a very good camera, of course; just perhaps not quite as good as it could be. -http://www.dpreview.com/previews/canon-eos-6d/6- DPReview
My FF upgrade will now be to a 5D2 - NOT the 6D! From my perspective the 6D is disappointing, DPReview summed it all up, "conservative, slightly unimaginative design that's become the company's hallmark." I have no plans to jump back to Nikon but Canon needs to watch their back. Technology moves ahead at warp speed and if Canon's stodgy approach continues, they may loose market share and eventually their dominance in the marketplace.
I feel like I am in the same boat. The 6D has some upgrades like:
-better focusing system (can't be worse than 5D2, and despite the lack of wider focus points, it covers same area as 5D2)
-slightly faster frame rate
-slightly better battery life
The DOWNGRADES, however, seem to far outweigh the positives:
-NO CF!!! or at least multiple card slots. SD cards are considerably slower and less durable. I have also invested a good amount of money in getting fast, reliable CF cards
I think the major determining factor will be how much better the 6D sensor preforms when compared with the 5D2 (if it even is better).
Hopefully by the time we get those figures, the 5d2 will be further discounted thus making my choice easier.