Yesterday Google announced a new feature for Google account users. If you sign up, each month you’ll get a link to a password-protected report that provides information on what you’ve done while signed in to Google.
The example Google gives is:
For example, my most recent Account Activity report told me that I sent 5 percent more email than the previous month and received 3 percent more. An Italian hotel was my top Gmail contact for the month. I conducted 12 percent more Google searches than in the previous month, and my top queries reflected the vacation I was planning: [rome] and [hotel].
To sign up, go to to www.google.com/settings/activity. Within minutes of signing up, you’ll get your first report.
More detail is on the Google blog: Giving you more insight into your Google Account activity.