Let's say you meet a stranger that gives you a bottle of orange juice out of the blue. You don't know anything about him, about his intentions or about the orange juice. Do you take it? Do you trust him or you refuse his offer, thinking that there must be some string attached.Google offers most of its services for free, you can use some of them (web search) even if you're not registered or if your browser doesn't accept cookies. They say: look, we have a free document editor online, would you like to use it? What do you do? You look at the privacy policy, try to decrypt the legal language or you trust Google and write private documents online?
"Google's servers automatically record information when you visit our website or use some of our products, including the URL, IP address, browser type and language, and the date and time of your request."
"We may use personal information to provide the services you've requested, including services that display customized content and advertising."
"We offer some of our services in connection with other web sites. Personal information that you provide to those sites may be sent to Google in order to deliver the service."
From Google Privacy Policy.