Thank you all for the quick and informative replies! Now the next question is, how do you convert a Nikon shooter to Canon? haha
If I were a Nikon Shooter, I'd stick with Nikon unless there were some particular must have feature that another manufacturer offered, and it was going to allow me to acomplish something that I badly needed to do.
The real world differences between Nikon and Canon cameras tend to be fine points that do not effect most of a shooters images.
Three years ago, video was one of the things that drove many to the Canon 5D MK II. Now, everyone has it, so its much less of a reason.
I maintain that 90% of the equation depends on the photographer using his knowledge of photography and properly getting the most of his equipment. Some get some pretty good images from a camera phone that I'd wished I had taken.
Sometimes, there are situations where having the right equipment can allow capture of a image in extreme low light, for example, but now, even a point and shoot like the G1X appears to take reasonably clean images at ISO 3200, so those barriers are going down as well.