Interesting NYT article on Sportsvision new camera system which will track player movement. Sounds like they are testing the system in San Francisco and then plan to install the camera system in all parks in 2010.
With this system it seems you can break down each fielder on the main factors: reaction time/speed/correct path to the ball. You can compare a player to the average and produce precise Defensive numbers. For instance you could take Scott Rolen and run a simulation with the batted balls faced by the Reds 3rd baseman and produce exact figures for Runs saved compared to a specific player or league average. It seems like they are open to making the data public and have the baseball community come up with interesting applications for the raw data.
This could be the biggest event in the baseball community since Bill James revolutionized offensive statics with his runs created formulas and innovative challenges to baseball orthodoxy.