Google is extremely open about what data it stores and makes it very easy to delete that data, but many people still don't realize exactly what's being stored, whether that information is given freely or deduced based on your searches.
A recent survey by the company Survata actually showed that the 2,500 respondents were more concerned about Google having access to their personal data than the NSA, their bosses, their parents, or their significant others:
In case you need the reminder...