I compared the same cameras, and bang for the buck, I choose the K10D. I feel it is more of what I want and offers more than the Nikon D40 or Canon XTi and after current US rebate will cost me only $530. That is less than half the cost of the Nikon D300 or Canon 40D, two other great cameras. At the local shop I visited and handled the cameras, the owner, a pro photog who uses Canon equipment, offered to me that he felt the Pentax is close to performance to the D300 and 40D at a price close to the D40 and XTi. He also offered that with today's technology all DSLRs produce excellent images so choosing any of these cameras was a good choice. The biggest factors for me were the backwards lens compatibility offered by the Pentax, and the big bright viewfinder when I compared them at my eye. There really is a big difference that I saw. And, the price which right now is right.
No real magic bullet answer, just some comments from my recent buying experience.