Mike Hendrickson at O'Reilly Radar – State of the Computer Book Market 2008, part 4 -- The Languages:

"If you look at the five-year trend for the languages shown below, you can see that C# has been steadily growing year after year while Java has been going in the opposite direction during the same period. PHP, ActionScript and Python are the other languages going in a positive direction. Ruby, Java, and C++ had the biggest declines in unit sales during 2008, and Ruby dropped out of the top 10 languages."