Digital downloads using the Marketplace plugin

Hi there ...

I'm working on a MU install - it would allow users to set up their blog-shop, to sell digital content, ebooks and presentations etc.

I want to use marketplace because it makes it dead easy to use custom-posts, in form of "ebooks" etc. Now the project rests on somehow being able to successfully allow an encrypted download link mailed out/file download allowed as soon as payment is made for an "ebook product". Kind of like graphicriver or other digital content sites...

Is anyone selling digital content using the marketplace?

All of the "showcase sites" seemed to be selling tangible goods...

The second less important request is, any theme suggestions for setting up a multi-blog ebook shop?

Thanks and best regards!