I've seen examples of the video showing vary bad wobble artefact form rolling shutter.
http://uk.youtube.com/watch?v=KcycneFY9lw
http://s477.photobucket.com/albums/r...t=DSC_0012.flv
I don't know if it's only on pre-production cameras but it looks awful.
Fine if you pan slowly, but for action (cars, skiing, MX etc) it's not going to work.

It's also half the resolution of the Canon video (740p instead of 1080p).

Biggest disadvantage to me seems that the Nikon has no external microphone input !
Canon have a mic socket so you can use shotgun, or a tieclip on your subject.

What has let down the videos I've shot with digital cameras so far is:
1) audio quality
2) no focus during filming (not even manual)
3) no zoom while filming (not even manual)

Nikon manages 2 out of 3, Canon 3 out of 3.