You are sort of making my point. They store the data on their devices and leave encryption up to me. How is this better than dropbox? It looks basically as easy to use as dropbox but how is it a step up?
A has files and gives B the key to the sync location. B enters it into btsync and chooses a folder. B downloads A's files over an encrypted channel directly from A's computer.
Add more people to get more to get multiple seeds.
Then they explicitely state that they store the data on their own servers. Is there another btsync?
EDIT:
Actually rereading it states they allocate space on their servers which sounds like they store data on their servers but I suppose it's also possible they might not.