well megapixels dont make or break a camera. and the more megapixels you cram into a sensor, the more noise you can have.
Schlyne, the reason being is that canon uses CMOS sensors which process images much better than CCD sensors. Nikon finally caught on w/ the D300 and D3. But these cameras are $1800 and $5000.
The canon 5D is 3 years old, 12.7 MP and a full frame sensor. Even though the technology is considered "old" it still pretty much out performs anything out there under $2200.
I will never switch to nikon, just due to the fast primes canon offeres: 35 f/1.4, 50 f/1.2, 85 1.2, 135 f/2...and if it weren't for having an intern, i would probably sell all of my zooms.
I have a friend who is a wedding photog who is a nikon shooter...everytime we talk, I get the vibe she is one ste closer to switching over to nikon.