[from Kent who found this on Tim O'Reilly's blog]
As you can see, the gains of C#, mentioned above, are even more striking than on the primary category treemap. While Java is off 10%, C# is up 78%. And that's without counting books whose programming language shows up as ".Net Languages." These are books that cover both C# and VB.Net. Combining these two categories, the C# book market is now actually a bit larger than the Java book market.