This is certainly exciting. It's the first attempt I'm aware of to quantify the defensive abilities of minor leaguers based on play by play data. Now that Minor League Baseball publishes play-by-play data, it's possible to use some of the same techniques we use to evaluate major-league defense to judge minor leaguers.
Obviously, the numbers published in the link above are subject to the same problems to which attempts to quantify major league defensive value are subject. They also have the problem of not being league-adjusted - players are judged relative to their leagues, even though it's clear that an average defender in the high levels of the minors should be better than an average defender at the same position in the South Atlantic League. Finally, the numbers only attempt to measure whether the player had a good year on defense. They do not measure whether that player has the skills to thrive on defense at the major league level.
But it's exciting to know that someone's taking steps to ensure that we no longer have to rely completely on eyewitness reports to judge minor league defense. This is especially important for prospects at the right end of the defensive spectrum (middle infielders, centerfielders) - if a prospect is a shortstop, will he be able to stick at shortstop?
Well, if the shortstops in question are Brent Lillibridge and Brian Bixler, the answer this study provides is a resounding "Yes." This data ranks Lillibridge and Bixler as the seventh and eighth best defensive shortstops, respectively, in the entire minor leagues.