Sharing documents through Google Docs is one of the highlights of the service. Unfortunately, there was recently a mix-up in Google Docs related to the feature, resulting in the files being made accessible to people other than those you've shared them with. The bug, which Google claims has already been identified and fixed, represents one of the downfalls of cloud computing - no matter what safety practices you use to keep your online data safe, there's always the risk that someone else could end up reading your words. To their credit, Google notified those affected and has taken care of the problem.
The problem was limited in scope, with documents being inadvertently accessible to people you'd shared files with in the past. Even so, there are often times when you'd want to share a document with one group and not another, so this still could have caused issues. As far as Google is concerned, you shouldn't worry about whether or not anything you are sharing has been broadcasted to an unintended audience, as anyone that was affected has already been notified. All in all, Google claims only "0.05" percent of the documents stored through the service were affected, though they didn't mention how many documents in total the service is responsible for.