It's obvious if you think about it, but this article drives some points home. If you use some kind of web service to read, listen, watch, charge, use, borrow or share stuff, that company not only knows what you've (read, listened to, etc.) They also know much more specifically how you did so: Did you stick with it to the end, did you do it from a particular place, at a particular time? Did you do it in one sitting or over a day or a week or a month?
If you then combine such observation across a farily large group of peope you can learn amazing things. Like how many people finish your book, or how far through it they get before abandoning it. Do they listen to the whole song? At what episode of a series do people abandon it? A little scary as the 'art' we 'consume' gradually morphs into the 'art' we 'like'.
Not only will be be offered to buy new products that we are likely to buy, but the products themselves will be designed in a way that we will like them. Or the art will be created in such a way that we will want to experience it.
Good or bad?
Scribd is just beginning to analyze the data from its subscribers. Some general insights: The longer a mystery novel is, the more likely readers are to jump to the end to see who done it. People are more likely to finish biographies than business titles, but a chapter of a yoga book is all they need. They speed through romances faster than religious titles, and erotica fastest of all.