Google lacks one thing that will prevent its true value from growing into its current market capitalization: trust. We already trust so much of our lives to Google. They know what we search for and do on the web, what we do with our time (Calendar), who we speak to and what we say (Gmail), and so much more.
People (and the regulatory authorities) were skeptical (and afraid) of Google's acquisition of Double-Click because of the "scariness factor." Soon, Google will hit a point where people will no longer trust it with certain kinds of information. People's lack of trust, or perhaps anti-trust legislation, will provide some setbacks for the company in due time.
Of course, this will leave "gaps" for more trustworthy young entrepreneurs to take the stage in certain areas; areas that people no longer trust Google to dominate. In reality, Google has nearly unlimited potential, but all-in-one integration in our lives can only reach a certain point before we become uncomfortable.