If there's anything more amazing than how the wheels keep turning, it's that we're sixty years into the computer revolution and people always think this is the last turn. I don't think we're quite done with the back-to-the-server swing (or "cloud" as they are called today), but a combination of still-ever-increasing horsepower available cheaply and the development of replication-to-the-cloud technologies already in progress replacing the only-in-the-cloud storage will bring a swing back to personal servers in the home. We're still in the early phases of this work.
I don't understand how my data is safeguarded by my home server when it's data I'm sharing with users who aren't on that same server. Once the data is shared, it's no longer under my control. I've wondered if there is a way to protect it, but I've yet to figure it out.
Of course, I'd love to find that there is someone who has a solution. I was unable to determine if buddycloud has figured it out.
There's no way to share information with another person and be sure it is protected, but if you do trust that person, then you can encrypt the data so only he can read it. All these new supposedly secure social networks still rely on the server admins and such not to look at or "lose" your information.
The problem has been discussed a lot here and I believe that you are correct that no amount of gymnastics will allow one to escape this dilemma.