I just got in touch with a Nikon user I know that I hadn't seen in a while. Well he got rid of his D200 and lenses and switched over to the canon 5Dmk2 :^( He wanted to go full frame and didn't like the D700 (Yeah I know, WTF?!) He's a great photographer and had been a loyal Nikon user for many years. It really surprised me that he switched.
But then, get this, I also found out that another long time die hard Canut couple I know is switching to Nikon! They're putting their 1Dmk3's up for sale and placed an order for some D3Ss! They were very disappointed in the specs of the 1Dmk4 so they're not upgrading. Now this shocked me even more so because they have been crazy loyal canon users for many years!
So what would make you switch sides? Honestly, don't tell me "I'll never switch" because all of us "have a price".