The only thing BT seems to store is your location (so they can connect any peers which use your key) and potentially the mechanism for authenticating the key th

The only thing BT seems to store is your location (so they can connect any peers which use your key) and potentially the mechanism for authenticating the key the other device uses to connect (it could be done client side but I dont think so). 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.