We learned this past weekend that "Google tracks nearly all your online (and some of your offline) purchases" through your gMail activities. In short, it means that Google reads all your emails. It also means that anyone with enough money (or potentially: hacking skills) can get their hands on that information.
The fact that you likely didn't know your activities were being tracked -- scanned, parsed, mined, examined, analyzed, dissected -- through your email content until now should be more worrisome than it probably feels to you right now. That's partly because the corporation has so far managed to convince us all that they will do no evil. Until 2015, the company's motto has indeed been "Don't do evil." One could argue that this motto is actually a warning that doesn't apply to the organization, but rather to its users (i.e., you.) Why should that worry you? Because the world changes every day. Every day a little faster. The meaning of "evil" inevitably bends along the curves of the politics of those changes trigger: what is understood as good today can turn out evil tomorrow.