Tim O'Reilly posted some
analysis and visualizations of book sales data
on his website. It
analyzed book sales trend in several dimensions. Java is shown on a
steady downward trend. On the other hand C# is clearly gaining share.
The idea is the state of book market would be a technology trend
indicator. Of course this is more likely to be a trailing indicator. Idea has
to be mature enough before it can turned into a book. And it would takes
months for it to be published and adopted in the mass market.
Nevertheless it gives a good picture what people are really buying into.