> On the other hand, the technology that Dropbox has mastered is so important that there should be an open source equivalent that we can all deploy, so we can have Dropboxes for sensitive info we don't want to share with them.

FTP?

Yes, I understand that Dropbox is a lot more than just FTP, and I love it, but if you're asking for a non-Dropbox dropbox... then you should just put an ftp server on an old box and be done with it.