RE: Can't you just lie?

Can you lie all the time when you are searching? Wouldn't that mean searching for stuff you are not interested in? If you are ill, searching for information on a different disease?

Not all data is asked for explicitly through a nice form where you can choose what you put. After a while, if you use Gmail, use a personalised Google search page and so on, they will collect lots of valid information about you and, depending on how clever they are, work out who you really are, whatever you put when you sign up.