Do the Nikons in that range have C class sensors? I checked out the D50 today in Costco, and it feels really cheap. This is where the Sony comes out way ahead, and so too for the Rebel XT--but that is comparing apples to oranges. However, the Sony feels in weight and quality more like my 20D with my 24-70 L than does even the Rebel XT.
I'm not familiar with the term "C class". I haven't handled a D50, but I wouldn't be surprised if it felt cheap - it IS cheap. The D70s, for the extra couple of hundred $$$, would probably feel better quality. I believe I remember someone here in the forums awhile back comparing the build feel of the Rebel and the D70 or D70s, and he thought the D70 felt much better built. It's more $$$ than than D50, though, and might be getting above budget after adding a lens.
I'm not stuck on any camera, even though I lean towards the Sony, so I'm up for more discussion for sure. The Nikon lens seems like a good deal. Given that it is nearly as good as a Canon L, I'd be willing to bet that the L lenses will come down drastically to keep people from moving to Nikon and the Nikon glass that is "nearly" as good as the L lens for 1/3 the price. So that too is a very positive point about Nikon.
In the interest of full disclosure, I never quite said "nearly as good as a Canon L". I've tried to find direct comparisons between Nikon & Canon lenses in the past, and been unable to, so I don't know how they directly compare. What I *can* tell you is that, while I haven't actually owned an L lens, I do own the Canon 28-135 IS, which is a particularly well-regarded consumer-grade lens, and I know that my copy of it is considerably inferior to the Nikon 18-70 DX in terms of image sharpness, as are all the other consumer-grade Canon lenses I've owned.
If you want an example of a photo I recently took with my D70 & 18-70mm lens, here's a crop of the full image (converted from RAW, a small amount of local contrast enhancement, standard sharpening w/PK Sharpener, cropped and saved as a jpg), taken from near the edge of the frame (which is always worse than in the center):
Here's a downresed version of the full-resolution image, so you can see how much of the image the crop represents:
Pretty good for an inexpensive lens, huh? (Especially since this was taken hand-held...)
Lisa