It seems logical that the easiest attack vector for any type of cloud storage is through social engineering. You're essentially protecting potentially valuable or incriminating data behind millions of dollars worth of firewalls, encryption and other technology... or a customer service representative paid $10-15/hr, if that.
Depending on how valuable the data is to you, it might be easier to just pay off a CSR, and then fake a phone call where you pretend to convince that CSR that you are that person. The person will get fired, but probably won't go to jail unless they can prove collusion. And then they can either find a new job, or depending on which country the person is living in, they can live nicely off of the money for a while.
I'm not sure how to solve this problem, except by having highly paid and specially trained CSRs that do the account resetting, or by never allowing resetting ever, and if you forget your password and your security questions, you're SOL.
I have to admit this only makes me more leery of putting anything on cloud storage, although my own personal data is pretty useless to anyone, which is my only saving grace. Others who are more important might need to think twice about relying on these types of services.