Re: And then billed 3 extra hours?
I seem to recall the clock speed on the Commodore PET could be increased by the simple use of a POKE command to a register. This was only safe for certain CPUs though, if you had the "wrong" one the chip would fry itself.
Biggest con I reckon with PCs was the so called "turbo" button which was nothing of the sort. It was actually a slow-down button for app compatibility.