The WSJ has an article on the data mining possibilities created by ebooks - Your E-Book Is Reading You.
In the past, publishers and authors had no way of knowing what happens when a reader sits down with a book. Does the reader quit after three pages, or finish it in a single sitting? Do most readers skip over the introduction, or read it closely, underlining passages and scrawling notes in the margins? Now, e-books are providing a glimpse into the story behind the sales figures, revealing not only how many people buy particular books, but how intensely they read them.
For centuries, reading has largely been a solitary and private act, an intimate exchange between the reader and the words on the page. But the rise of digital books has prompted a profound shift in the way we read, transforming the activity into something measurable and quasi-public.
The major new players in e-book publishing—Amazon, Apple and Google—can easily track how far readers are getting in books, how long they spend reading them and which search terms they use to find books. Book apps for tablets like the iPad, Kindle Fire and Nook record how many times readers open the app and how much time they spend reading. Retailers and some publishers are beginning to sift through the data, gaining unprecedented insight into how people engage with books.