I just heard, that something like "New Generation Game Demos" are coming - first to Playstation 3, then to Xbox and then to PC.
These new game demos are quite easily explained:
The "Demo" would actually be pretty much full-game BUT - the longer / further the player plays it, the more gameplay and stuff the player will miss.
For example Final Fantasy demo would work as the full game and it would be full game but your weapons would get weaker the further you play it.
Another example would be GTA, the longer you play it - the crappier the cars would get.
This new demo-system is in development because the companies want to give players the power to choose what they want to test in the game, before it comes nearly unplayable.
Now, I don`t know how this would take effect against pirates - will they just crack the demo, or actually buy the game after the exclusive demo?
Either way, I think this is a creat idea!