From that StackExchange link, the top-ranked answer has the following comment:

"However, one more attack: an attacker can guess plaintexts and test if you have that file."

If that's the case, pirates beware.

Yes, there's exactly the same problem as with Freenet. Because same plaintext encrypts to same ciphertext there is huge problem with that. If I really don't anyone want to know that I got this data, that's failed scenario. It makes things easier for service provider, they don't want to know what they're storing. Just like Freenet's data cache. But if I know what I'm looking for, I can confirm if my cache contains that data or not. Therefore this approach doesn't remove need for pre-encrypting sensitive data. Otherwise it's easy to bust you for having the data.

Edit: GNUet quote:"The gnunet encryption scheme is remarkable in that it allows identical files encrypted under different keys to yield the same ciphertext, modulo a small block of metadata. These files can then be split into small blocks and distributed (and replicated if need be) across hosts in a gnunet system to balance load."

http://grothoff.org/christian/esed.pdf Efficient Sharing of Encrypted Data - Krista Bennett, Christian Grothoff, Tzvetan Horozov, Ioana Patrascu