I really wonder how you can efficiently implement this use case:

"Show me the flickr photos that my friends and the friends of my friends faved in last 2 weeks, sorted by the total number of favs", while the photos are still stored on flickr.

I can see you can implemente that with "agent" that will crawl to the hosting sites of your friends and their friends, collect the data and come back. But that would be slow, especially if some of your friends host their data in PCs that are currently offline (remember The Eight Fallacies of Distributed Computing?). Do you have any solution for that in mind?

BTW, creating a Virtual Machine you still provide API to the applications. But it is quite broad, which means it is difficult to control security.