The new feature tracks every search a registered user makes and lists them on the My Search History page. Users will be able to pick out a date and see which searches they made and on which sites they clicked. But you also have the option to disable the service or to remove particular searches from the history.
Marissa Mayer, Google's director of consumer Web products, said the service allows people to use what they've searched in the past to build more intelligent searches.To be able to use My Search History you will need a Google Account, which will also gives you access to other services such as the Video Upload Program.
More info at Reuters or at Google's Search History FAQ