I always admire people who can try several brands, but don't fully understand it. I have a significant investment in Nikon bodies, lenses, accessories, flashes, etc., not to mention a LOT of time learning the unique features and abilities of the gear. I couldn't easily switch from one brand to another, but also am happy with Nikon.I have owned Nikon (D80, D300) and now use Canon (40D) so I can speak
to your questions from my own experience.
Having owned a D300 and a 40D, I would say the weight difference is
not very much. Both are very solidly built cameras but the D300 has
more robust weathersealing and additional features so the added
weight is understandable.
HOWEVER, with the new K7, Pentax has shown that you can build a
feature-rich DSLR that is roughly equivalent to the D300/50D in a
much smaller size while still maintaining a large viewfinder, LCD,
and a good control interface. I find the D300/40D too bulky given
their substantially smaller sensors and mirrors compared to full
frame, so I hope Canon and Nikon learn their lesson from Pentax for
their future models.
Regarding your last comment, I would just say, "One interesting body does not a system make." Personally the size doesn't bother me.
--
JohnE
I have enjoyed taking these images: http://www.pbase.com/jpower
Below, Phoenix City Hall with Nikkor 10.5mm on D200