Google is a search engine which does not see any boundaries, unless and until you show it some barriers, by blocking it using robots.txt. Many of us, including webmasters, like to have Google index our content as soon as possible.
However, some of us would prefer that we are not on Google. If you are someone who does not want to show up in Google search results, the Wired wiki has a nice little article which will show you how to Un-Google yourself.
They cover using robots.txt as well as social networking sites like Facebook and LinkedIn, so that you are covered all around. However, if you want to stop Twitter too, all you have to do is to convert your account to a protected one.
Another interesting point covered in the article includes how to choose smartly between image sharing websites, lest your wedding pictures make it to all of the Internet.