I don't want to beat anyone up, but I have had no such problems, and have found no conditions to date where my particular K5 has not performed to my satisfaction. For those with problems, and I don't question their honesty, I hope you can get a resolution either through a new body or service. It troubles me that someone might be missing the satisfaction I am enjoying with this fine camera.
When the FF issue appeared to sour my desire for the K5, I was at the edge of buying a D700....and every day I thank my Lucky Stars I didn't. For those that live by shallow DOF, the D700 would be a good choice, no doubt, but for the vast majority of shooters, I think the K5 beats it easily. Considering the ISO abilities of the K5, the price, and the fact that you don't need a forklift to haul it around, the great IQ, and the efficient ergonomics of the K5, it is no wonder I thank those Lucky Stars!
Best Regards