Interesting but wonder if this type of encryption ruins Dropbox business model since it keeps them from de-duping anything. I couldn't care less about Dropbox's business model... just curious.
Of course any kind of encryption does make a dent in Dropbox's margins, since Dropbox's model is to dedupe data across all its customers but yet charging everyone as if the space used is strictly by their data alone. But the follow up question would be how much of personal (non-public and non-shared) data do people store vs. how much publicly available or shared data (not necessarily free) data they store in their Dropbox accounts for this to make enough of a dent.
I doubt Dropbox gains much from deduping between customers, but I'd love to see some data to the contrary. Last I knew they weren't sharing that, but most of my data is unique to me and anything I'd want to encrypt is unique to me.
I think they do gain a lot from selling 2TB to people using 30GB and selling additional users of the same <3TB of data to enterprises. (That's gotta be pretty sweet profit if they have takers - $12.50 more a month for zero additional storage and a little more data transfer.)