For now I'm going with Bittorrent sync [1], at least until an equivalent service with an open source comes along. (Would be nice if they open sourced theirs, though.)
I'll be limiting my use of it and hope that ClearSkies goes well.
They provide discovery, syncing & NAT traversal to a hard drive that you own.
https://github.com/calmh/syncthing
git-annex with the assistant was supposed to be a dropbox replacement too but I haven't had much luck with it.
The developer is awesome but he seems to be going at this from "how can I make git more userfriendly" instead of "how can I implement a dropbox that just happens to use git". clearskies/btsync/syncthing won't inherit all the great git stuff (great versioning mostly) but they seem to be more on track to give a good user experience.
Something like tarsnap is the only paranoid-proof choice. It's not even distributed as a binary file.
And they can be ordered to do so secretly with no notice, neither to company management nor to you nor to any judicial body that could review the decision.
That's the lesson of Lavabit.
Now, I don't believe that they'd do this maliciously (rogue employees aside), but there's always the possibility that a government agency could secretly require them to actively try to capture a particular user's password the next time they sign in.