Nikon's lousy customer service
One of the reasons I decided to go Canon was Nikon's insistence that to download a full, printable copy of a camera manual, one had to enter a serial number. That's hogwash. I was able to download Canon manuals with no problems, and evaluate the functionality.
And so, Nikon, you lost about $60,000 in sales from me.
I'm surprised to see that Nikon are requesting a serial number, I've downloaded manuals for D100, D3 and D7000 without any such requirement (from Nikon USA site.) I saved them as PDF files then used Acrobat Reader.
In any case, it seems an unusual way to determine which Camera to choose...