Valve have announced a beta of a new system called Guest Passes in their Steam digital download system:

Later this week, new menu options will appear within Steam as we initiate the closed beta for Guest Passes, a new feature that will allow owners of certain Steam-enabled games (purchased either via Steam or at retail) to send a friend limited-time trials for those games.

During the beta period the new menu items will appear on all Steam accounts, though the ability to send the Guest Pass will be inactive. When this closed beta concludes, Valve will extend the Steam Guest Pass Beta to Day of Defeat: Source owners.

A "limited-time trial" sounds like a demo, only less good.

You're right, that's terrible

only took 4 days to finish dark messiah of might and magic.. why would you buy a game when you get a week or whatever "limited time" to play and finish the whole game in that time....

I suspect it'd be around 60 minute time limit rather than a week for that very reason

I suspect its more for multi player games than single.

spose... they could do it that you have access for a week but have to log back in to the game every 60mins... prolly pop up some adverts and sales propaganda

I like it in the way that Ive bought many games and hated them after a few mins play.