Book sales trends

Book sales are a pretty good barometer of what's going on in tech. The nice people at O'Reilly track these trends and there's a graph and a short writeup in “The Rise of Open Source Java” at the O'Reilly Radar. As the title suggests the trend is towards open source Java books, but it's interesting to see Python gaining on Perl and Visual Basic®—the COBOL of the future—in steady decline.