There might be some limits with certain lenses, but so far, I've found that all of my K-mount lenses (not many, maybe five or six) are usable with my K10-D. There is an option in the K10-D menu that allows you to use the aperture ring. And then you set exposure by turning the dial to "M" and pressing a button on the top deck. It's an excellent setup.
The only downside is that the focusing screen for autofocus SLRs (any brand) isn't ideal for manually focusing a lens. You have to focus much more slowly and precisely than you would with the LX.
And if you have an M42=>K-mount adapter, you can use M42 lenses, as well. They have to be used in stop-down mode, so things really slow down.