Some of the most interesting data on trends in mobile development has been coming from Flurry, an app analytics company (developers insert little snippets of Flurry code in their apps to gather usage data).
They’ve plotted frequency of usage against app “retention” (what percentage of buyers returned to the app within 90 days of downloading it), and put each category of app into a corresponding quadrant:
They note that books fall squarely into the “use a lot for a short period of time” category, which is not unexpected:
In Quadrant II, we find categories like Books and Games, among the two largest app categories in both the App Store and Android Market. These application categories are characterized, on average, by intense usage over a finite period of time. Because games and books offer content that typically is consumed only once, the user usually moves on after reading a book or finishing a game.
They also draw some interesting conclusions on which categories are suitable for subscription vs. a la carte models.
Note this data comes from the set of apps using the Flurry software (they say more than 2,000), so is by no means a scientific sampling. Interesting reading nonetheless.