This FORBES article that's coming out is so obvious: these guys see are probably already seeing people jump ship. People probably have mostly music in their dropbox accounts. Once Apple releases their ITUNES MATCH for $25 annual product, people will be dropping off like rats on sinking ship.
I know no one who actually uses their Dropbox in that manner. It would seem like a very silly way to use up all your space when most people think music is important enough to take up the majority of their local storage. I don't see the appeal of all these music locker services when local storage is increasing every year.