While I'm a big fan of open source in general and of using standard components yadda yadda yadda
For me the biggest draw of Dropbox is that it's not self hosted but that it's run by an entity that's 1) large enough to not go away any time soon, 2) fairly unscary (unlike, say, facebook), and 3) 100% dedicated to keeping the service running so I don't have to worry about my files anymore.
Self hosting only gets you 2).