I personally haven't done this but you bring up a good point.
What is so crazy about releasing a fully playable free demo that lasts 10 days that enables you to save your progress and pick up where you left off after purchasing the full version?
No doubt a system like this would have multiple weaknesses but if this system existed I can guarantee you that I would own more games.
Sony is starting to implement this sort of feature with the PS3. You can download the entire, full version of the game to your console, and then you have 24 hours from the first game start to play the game, including saving your position, as much as you want. Once the 24 hour period is up, you can keep your game saves, and either delete or purchase the game, at which point you can continue from your game saves.
It's just too bad so far that you can only do this with an extremely limited selection of games that have already been on the market long enough that I would have bought them if I was actually interested in them.
What is so crazy about releasing a fully playable free demo that lasts 10 days that enables you to save your progress and pick up where you left off after purchasing the full version?
No doubt a system like this would have multiple weaknesses but if this system existed I can guarantee you that I would own more games.