There was a game a long time ago, Star Control, I think (I still have the box, so I guess I could check...) that used a special 'linguistic translator' to provide copywrite protection. It was essentially a series of paper wheels all aligned on a single rotation point. In each wheel, slots were cut and words were printed. The idea was to make specific challenge-reply series match up to arrive to the correct password.
Very cool and it helped immerse players, but unfortunately I think that with today's means it would be pretty easy to crack. However, could there be an equivalent device for our times that actually ships with the game? Perhaps a small and inexpensive USB key that actually holds a key encoded or a chip card reader? So long as you have the USB key with you, you can install to any computer you want.
Hackers will likely crack this in 0.00000002 nanoseconds, but any thoughts?