Interesting discussion here. I think that comparing Nikon and Canon, beyond a certain level of camera---in terms of quality image production--is like comparing tweedle-dum and tweedle--dee. Pros ("real" pros working for very high end employers) use both systems. I own both a Canon g12...which i use exclusively underwater... and a d300....my topside camera.
Of course, one cannot reasonably compare a d 300 and a g12. they are aimed at different markets. But you will find pros who use top end of nikon's stable and those who use top end Canon cameras all over the world. I'm not sure that Canon owners are quite as smug about their equipment as us Nikon owners are, but I can't say for sure since i know about 10 nikon owners for every canon owner i know.
The bottom line may end up being service, i.e., how does each manufacturer treat you as an individual customer. I am an american who retired about a year ago from the public university system in NY. Now i live in the southern Philippines. I arrived here with my D 300 and it has needed nothing in terms of service since i arrived. I purchased a G12 Canon last april and it, also, has performed without a need for service. I have bought other canon products since i have been here and my significant other, who owns a several years old canon point and shoot, has interacted with the Canon Service Center in Davao...the country's second largest city. I must say that, in spite of not being Canon's headquarters here in the Philippines, the Davao Service Center's service has been exemplary--much, much better than I received from Nikon (no more than a couple hundred miles from their east coast service center) in the USA when i had occasion to need help from Nikon.