Just an idea, tell me if it's old or nonsense
There are lots of cloud storages around, Dropbox, Google Drive etc. Also Bitcoin-payed like CrownCloud or Wuala. But Wuala is different, it is encrypting the data at client side (SpiderOak too, don't want to advertise). Still with their user-side encryption, they can de-duplicate the data. I found that really cool, let's imagine:
Imagine a "real" cloud storage, I mean a P2P network like eDonkey or BitTorrent. Your data is somewhere in the community, but it's safely encrypted! And a guy having loads of space, why should he share his drive with the network? Because he could get Bitcoins for it! On the contrary, someone wanting to store even more in the cloud than on the device could pay for it.
Technically I would split files into 4k chunks if it doesn't influence cryptography too badly, but deduplication would be better (lets say you changed few bytes in a 1gb file). The hash of it (MD5 or SHA1) gives the password for a symmetric encryption. The checksum of the encrypted blob again is used as an id to ask the network for data. Same data gets encrypted same way, thus deduplication possible. A "file" is basically the list of blob-ids and their passwords, symmetrically encrypted with your private global password.
I don't know yet how Bitcoin comes now into place. A payment to somebody to download some of the blobs sounds like spamming the blockchain with way too many transactions. Maybe a kind of pool would help?
Well but maybe there is just no market for a Open Source P2P storage, as the commercial ones are too many and too cheap..