“When it comes to buying apps in the iTunes App Store, books are the most widely available, but they’re also the apps least likely to be purchased, according to Apptizr, an iPhone application recommendation service. It found that 22 percent of all available paid apps in the App Store are books, yet they account for just 3 percent of all app purchases.”
GigaOM presents a break down (with a graph) of which apps are selling and which apps aren’t, showing that people much prefer iGames to iBooks.