For years, sizing up the media's shortcomings has been a popular if fuzzy sport, full of subjective observations, grand generalizations, and polemical abstractions. Al Franken, for example, is happy to tell us that "Rush Limbaugh is a Big Fat Idiot," but he never tells us precisely how big, or how idiotic. Ditto for Bill O'Reilly, who warns us of the media's anti-Christmas bias. But he never gives...