From that uber-forecaster and sometimes ESPN contributor Nate Silver (Insider access, required):
Yankees (2008 FRAA: –26 2009 Projection: +9)Sorry to get all "statty" on you today, first with WAR and now with FRAA.
First basemen are rarely impact defenders, but two-time Gold Glove winner Mark Teixeira is a significant exception. Plus he replaces Jason Giambi, who had only slightly less range than the Miller Huggins monument at Yankee Stadium. If Jorge Posada has trouble coming back from right shoulder surgery, take note: Backup José Molina, one of the best defensive catchers in the game, threw out 44% of potential basestealers last year.
[Note: the Fielding Runs Above Average (FRAA) metric measures the runs saved or lost relative to the MLB average]