The problem with cloud stuff when it comes to security for me are two things. For one, they surely are out of business if they get hacked - and it gets public. So would you trust them to tell you about a security breach when they can try to hide it? Another thing is that you don't know about their business perspective. I can vividly imagine that some are willing to just take the risk of getting burned in hell for short term profit. The risk I personally fear the most is the non hacker inside security breach. So, you know someone working in a company that does data storage and has administrative access. How much do you need to offer or how well do you need to know him? Or is he trustworthy in the first place? From a professional and a personal perspective I don't trust anybody, based on experience. And the problem with this scenario is that it does happen but no one can really tell how often and with how sensitive data. So yeah, if your data is really confidential and critical I wouldn't take the risk of big cloud storage.