This comment is also legendary misunderstood. He pointed out how trivial the idea was, which of course became a problem for dropbox when every tech company implemented it once they saw the demand for it and took its marketshare. Nowadays it's hard to consider dropbox as anything but a dying product of a dying company.
For a Linux user, you can already build such a system yourself quite trivially by getting an FTP account, mounting it locally with curlftpfs, and then using SVN or CVS on the mounted filesystem. From Windows or Mac, this FTP account could be accessed through built-in software.
[1] https://news.ycombinator.com/item?id=9224