Catchers are sort of the final frontier for defensive metrics, but some interesting results have come out in the last year or so. Today Bojan Koprivica at The Hardball Times went Isaac Newton on the problem of pitch-blocking. In summary, it looks like an actual skill, and over the course of a full season, someone who is really good at might win an entire game more than someone who isn't. This could be a final move toward overall scores for catcher defense, some of which the article breaks down by components.
I'm sure what everyone most wants to know is what this will do for Jeff Mathis's case for a Gold Glove. Well, he comes out at as just about average: 23rd out of 60 qualifying players over the last four years. Although better than previously believed, the metrics suggest that in exchange for tolerating his miserable bat, Mathis has rewarded the Angels with all of two runs better than the average defensive catcher, and six runs better than Mike Napoli.
That's spread out over nearly 650 games. Considering that Napoli has been almost 150 runs better with the stick during the same time, Mike Scioscia and the astroCERAlogists are still off by a factor of 25.