When Canon offered 21Mp senzor the Nikon's users said the same because they had only 12Mp at that moment. And Nikon was leader in high ISO ...
I would never really consider a 40mp 35mm sensor. Not until a second generation version at least. Image quality is king and even with my 1Ds3 I've taken landscapes that print a meter wide.
High MP = Small pixels = not good for IQ
Let's wait for proff reviews and comparisons
The 3500US and maybe 3500 EUR here is huge in my opinion. For the moment 5D2 is great.