"Google's newer services only increase the potential for harm. For example, the brand-new 'My Search History' service keeps a record of all your past Google searches. The benefit to you, the user, is that you can easily zero in on a past, successfully refined or complex search without having to recreate it from scratch.
But the downside is that Google can retain a full record of every search you've done on Google. And because 'My Search History' requires a login, that information isn't anonymous. Rather, it's tied and trackable to a specific user--you." (more)