Shortly after launching a state data portal, the state announced the Apps for Californians contest to encourage programmers to use the available data as raw material for building interesting applications.
One of the entries, Explore California, plots out county and state stats to illustrate trends in population growth, personal income, unemployment and other demographic data for the state and its 58 counties. While the data only goes through 2007, it's an interesting and useful way to look at county trends over time.
Other entries make use of social media and education data. One even shows fishing spots. One mobile app culls data to provide users with what the developer calls "a Geiger counter for crime" that scores the safety of the current neighborhood within San Francisco.