The Takumars seem very sought-after by some digital user communities, but not others. I hear the Sony DSLR forum regards them as the spawn of hell, for example. Given the results I've had from a 1960s Auto Takumar 55mm on my K-5 before now I can only assume that the fault doesn't lie with the lenses...

M42 lenses will always be in demand as there are adapters to fit them to pretty much any current system (and most older ones too). I know there are glass-free adapters to fit them to Canon DSLRs as well as the Pentax ones.