Max Marchi investigated the accuracy of the PITCHf/x plate location data. Max used a technique similar to mine, and in fact, I have an article planned soon to go into more detail about my method. Max, however, added a helpful feature, using multilevel modeling.
Kyle Boddy wrote about how to measure pitching mechanics and the challenges involved in gathering and using the data. I believe this is one of the next frontiers for baseball analysis after, and perhaps alongside, learning to digest the detailed ball tracking data like PITCHf/x.
Carson Cistulli applied his historical groundball percentage estimator to identify the most groundball and airball-prone pitchers since 1950. Carson links to some discussion of the development of his estimator, and those discussions are well worth reading if you're interested in more depth on the topic.
J-Doug Mathewson took some of the concepts from my article on the real umpire strike zone, combined it with his previous research on the topic, and quantified the advantage that pitchers get by targeting the edges and expanding the zone.
Josh Smolow cracked open the enigma that is Carlos Marmol and dissected some questions about the battle between batters and Marmol and why they lay off the pitches that they do. Josh both reveals a lot about why Marmol has such high walk and strikeout percentages and also raises some fascinating questions about why batters behave the way they do. I have the feeling there are some key concepts for the future of sabermetrics in this article, though I haven't quite been able to pin them down in my own head yet.
Jeff Zimmerman did a detailed comparison of the pitch framing work by Jason Kendall and Brayan Pena for a number of borderline pitches from Zack Greinke. Jeff doesn't have a grand conclusion about which catcher is better and by how many runs, but he does an excellent job of laying out how one would do the yeoman's work of tackling this topic and documenting the catcher mechanics involved.