Google is amazing for searching the public web. It contains all the weblogs, websites, videos, and images that are shared by everyone. Everything Google can get its hands on, will sometime or another be found by someone that searches for it.
The problem for Google however is, is that it can't cross the borders that are created by some websites, like Facebook or Hyves. And sometimes the borders are really low. If there is a just a little border, Google can't get to it.
In one way this is a good thing. I really like it that other people can't get to my private stuff. However this problem also excludes people who can normally see my 'private' stuff, to search for those things in Google.