Cloud services provide great help but blindly relying on their security doesn't make sense. If you built the system ground up, you'd take time on security so you should do so with your data no matter where its located. Tools like BoxCryptor (or encfs for us diy folks) make quick work of securing remote files. If you store trade secrets or pass sensitive information through cloud services, you should consider the risk/reward of choosing those over a solution you can have more control over (and consider if there's an option to secure your data). While remotely hosted applications can make life easier, you need to always consider that security and convenience are at odds.