I currently own 5D Mark II, the reason I stick to Canon is the lenses I bought over the years (couple from film slr days as well) but few of my kakis are D700 users, I think both Nikon D700 and Canon 5D2 are great (not just good but great) cameras and both have their strength and weakness we should not get ourselves confused trying to determine which is better.
The decision should be base on your preference of the system beyond camera body, your current lenses investment and your style of shooting. I realized Nikon system present you a very highly customizable setup where you can almost tweak everything and anything, many many buttons. Canon go for very simplistic design and only present it users very limited customizable set (technical folks won't be happy) but the strength lies in the core features that they did really well.
Similarly, there are people that like Home theater setup with highly customizable features, many speakers and many many buttons and there are some that love HiFi very simplistics look and purist operation no treble, bass, balance controls only one big volume control knob, it is a matter of taste and style. It is like Mac and Linux, we can argue till the cow come home.
I personally, like Nikon, Canon and even Pentax very much, but probably one should consider buying what their kakis have so it will be easier to get peer support and tips.