This is how Bitcasa is working I think. You would see all the files, in a fake hard drive of unlimited space. Some magic (machine learning and smart decisions) would try to figure out ahead of time my data access pattern.

So I would see all my pictures list, if I decide to open the first one, it would take a few seconds to download, and then I start browsing the pictures, it would figure out I plan to look at all of them, and pre-fetch them from the cloud, so there would be on average no perceived latency.