Gizmodo has just posted a great comparision review between the Canon 5D Mk II and the Nikon D700. They conducted several real-world tests on both cameras and outline the pros and cons of each.
Overall they plump for the 5D, mainly due to the ability to switch between still and HD 1080p video using a 35mm lens. The D700 does come out better in some of the tests though, such as high ISO.
Click through on the link below to read the full review.