I think both systems have their benefits and as Bushnuts mentioned, one will always try and trump the other.
Having used the D300s - I think it's a fantastic camera. But noise-wise there isn't that much difference between the photos I took with the D300s and the 7D. Therefore in that class-range of camera I will go for the 7D due to the 18megapixels versus 12megapixels. I get what you said about the eye not being able to really distinguish, but when I'm in KTP with only 400mm focal length, the extra 6mp goes a long way in giving me quality usable pics even if cropped 50% (which will make the resulting photo still come out at a whopping 9mp!)
This also helps when photographing small birds that aren't sitting right next to you.
As mentioned I am planning to one day move over to Nikon - it might be soon but at this stage it's unclear. When I move I will not settle for less than the D3s and the 200-400mm f4 lens which is about as tack-sharp as any prime I've seen. But that is big money. My ideal Nikon kit would be:
Nikon D300s (backup body and for using 1.5x crop on the 200-400mm lens for longer distances)
Nikkor 200-400mm f4 VR II for general wildlife and birds
Nikkor 70-200mm f2.8 VR II for close-up wildlife and birds
Nikkor 14-24mm f2.8 for wide angle landscapes
Nikkor 24-70mm f2.8 for general landscapes and portraits
and hopefully one day a Nikkor 600mm f4 VR II for birds and long-distance wildlife
But yes, that is a lot of money and probably wishful thinking.
I have already ordered my 7D plus battery grip, and a Canon 10-22mm wide angle lens plus polarising filter as I need a better camera NOW before my next trips, and as BushNuts mentioned I have some lenses already. I can always sell my stuff if/when I move over. But I will by no means discourage people from buying Canon cameras and lenses. From various reports/reviews I've read it also seems that Canon lenses get more dynamic colour range from an image/scene than Nikon lenses, although the Nikons seem to have the edge in sharpness.
If I stick with Canon I would like to move to the following kit:
Canon 7D/Canon 1Dmk4 for wildlife
Canon 5Dmk2 for landscapes
Canon 600mm f4 L IS for birds and long-distance wildlife
Canon 100-400mm L IS for wildlife and birds
Canon 70-200mm f2.8 L IS for close-up wildlife and birds
Canon 16-35mm f2.8 L for wide-angle landscapes
Canon 24-70mm f2.8 for general landscapes and portraits
Canon are getting better at the high ISO capabilities of its cameras and the AF on the 7D/1Dmk4 is already right up there. It would be interesting to see if Nikon take the megapixels up to 16 or so in the D4 and D800, and keep their ISO performance so stellar.
I hope this makes sense?