I've been told that the hobbs on an MU-2 is on the gear. No idea of the truth of it, but the story goes that some genius "borrowed" one to go visit his girlfriend and just flew over with the gear down. Just so happened that the DO was in town and saw "his" airplane sitting on the ramp...hilarity ensued.
As to high time aircraft, for my own part, it would depend on the maintenance and history of the airplane. I've flown a 45,000 hour BE-99, and while it was far from pretty, I didn't have any concerns about its airworthiness. I've also seen some 10,000 hour flight school planes that would have me packing the car for a long drive.