Imagine a game streaming service like On-Live, but; you don't pay a subscription to stream full games and instead play demos for free, afterwards there's store after playing to see if you want to purchase this game in a non-stream format.
http://www.pcgamer.com/2011/02/28/play- ... in-needed/
Gaikai is a new online retail solution which is under open beta in America, I cannot join at the moment as I am not situated near a data centre. What I understand is that all you need is a fast internet connection, java and flash.
http://www.gaikai.com/about#general
I think it's a cool idea, quicker and more effective than downloading GBs for a 30 minute demo. If this gets enough exposure I see that it'll be widely used... as long as the purchase offers choices off-suite such as D2D and STEAM. We don't need another dedicated online retail store.