There have been years and years of these Nikon vs Canon posts. There seems to be kind of a pattern to the professional reviews of these brands over the years as well.
1. Canon generally is ahead in the spec war, with more MPs per dollar than Nikon. Canon introduces higher MP designs earlier than Nikon.
2. Nikon seems to be more concerned with noise and artifacts than in pure MP power. The FX spec D700 is "only" 12MP, half that of Canon, for example.
3. Canons have more in-cameral sharpening and more saturated colors as a default. Nikons output a more subdued image, expecting post-processing.
4. Nikons generally are more ergonomic in terms of how the controls work and the menu system is usually less imposing.
5. Nikons usually seem to have a better build quality feeling to them. Even the entry level plastic D40s and the like are very solid feeling.
6. All in all, Nikon is a more conservative company, Canon more apt to dazzle people.
Something for everyone and if you love your equipment, then it is likely you will use it better.
One thing is missing, from what I can see, and that is reliability. Which brands are going to fall apart on you? Which companies have the best warranties and repair service?
Ken? Hey Ken! Yea, you, Mr. Rockwell! 'Sup! Welcome to the forum.