During the past week (October 2014), I have seen two instances of the public document sharing portals being hacked.
First it was Dropbox and then Apple in China. It doesn't take too much to see that public sites are attractive to hackers because of the size of their presence and (in Apple's case) possible linking of other personal data.
Both of these above mentioned environments (and indeed most of the public file sharing portals) were designed for comsumer usage, not business to business. The inherent sharing and data integration capabilities are not there yet.
No doubt that these companies have the resources to catch up, but it requires a different platform model to embed these within a business environment, and that means significant changes to their core platforms.