Between the National Security Agency (NSA) and Google's own overreaching terms of service, your files on Google Drive may be open to snooping from both organizations. What are the risks and how can you minimize them?
If you store your files on someone else's servers, then they can access the files. Either law enforcement can make them do it, or the server admins can steal your data, or just expose it through negligence. The best way to protect files is to use encryption, but it must be done locally, not on the cloud server. There are many tools that will do this: Truecrypt http/www.truecrypt.org/ will encrypt entire disk volumes. Syncdocs http/www.syncdocs.com/ will encrypt files stored on Google Drive.