To all the "no problem", "I don't care", "everybody does it", "nothing new", people: the disturbing thing here is of course that this system can and will be used for political prosecution purposes. The marketing tool can, with the flick of a switch, be transformed to an effective purification tool. And, with the historical data available, this can be done with retroactive effect. It would all too easy to write some software that sets the bad people apart from the good people. It takes only a little historical awareness to send shivers down ones spine. Orwell's 1984 is a fairy tale compared to this realilty. Unfortunately, very little Americans poses this awareness and your modern times educators (Facebook, Google and the like) will not be particularly keen on providing it because it is a thread to their business model.
I really have to wonder what people do online. If you're concerned about business information being "looked at" in your e-mail, you probably aren't using gmail anyway. If you are, your e-mails really aren't that important in the grand scheme of things.
Other than that, what are you worried about? Are you doing drug deals and plotting murders through gmail?
Google needs to pay for the costs to maintain a huge e-mail system. Since the service is free, they're looking to offset the costs via advertising. Office 365 costs money, so you don't get ads. It's that simple. Why can people just not see that a 'free' service costs you something at some point...?