Are you aware that gmail keeps all of your emails, both incoming and outgoing, indefinitely even if you delete them?
All the emails that you have ever received from all your friends and contacts and all the emails that you have sent to any one else, including all the attached documents and images, are being archived by them.
This is the same for their Google search engine: every time you search for words they register that and archive what you have searched for and your ip address. They also register what link you click on based on the results and store that information too. I'm not referring to the local cache on the PC and internet browser, but to their own database.
There are some agencies, after asking a hefty fee, can find information about someone through those archived data and present it to a potential employer for their scrutiny.
How do you feel knowing that all of your internet activities are logged indefinitely and might be used against you in the future?