Tim O'Reilly posts on State of Computer Book Market , O'Reilly research along with one another company is doing market research on quantifiable metrics about the state of technology adoption. His posts shows some data on how the book buying trend is going on and what OS book sell the most. Quite an interesting graph, I was not thinking that MAC OS X will have such a huge share!!
Also what I will be interested is a graph or some figures that shows how many people are reading ebooks, subscribe to services like Safari and other online ebooks provider and how many books do they subscribe too, that would be something interesting to look at.
Tejas Patel