Mark, although I am a "Canon guy", I am first and foremost a gearhead (cameras, backpacking equipment, car parts, whatever...). So I'm not loyal to Canon if the competition comes out with a superior product. The K10D is less expensive than my old 30D (sold it), yet trumps it significantly in features and capability. I did have to invest in a new set of lenses, but once again, if Canon had come out with these ultralightweight limited primes, I would have bought them from Canon anyways.
Regarding the size (and weight), the camera is comprable to my old 30D. But, of course the K10D has greater resolution and builtin IS. Add an IS lens to the 30D, and your packed weight goes up significantly, and will be much heavier than a K10D rig weight. I rely on IS, as I don't usually backpack with a tripod...
Finally, the images from the K10D are impressive. I have been spoiled by the amazing noise characteristics of my 5D, but as I primarily shoot landscapes with the K10D (hence low ISO), this is not an issue for me. I do shoot weddings and portraits professionally, and wouldn't recommend this as a wedding/action camera. But as a landscape tool, there isn't a better DSLR on the market at any price. The weather sealing, sensitivity modes, dedicated bracketing button, builtin IS, light weight, limited lenses, etc, make this system irresistible (to me) as a bakpacking rig.
It also handles skin tones well, and images have a warm, filmlike feel. Hard to explain. Here's a recent candid shot from a photo shoot a couple weeks ago that may give you a sense of what I'm talking about: