Cookbooks are strange. With the number of recipes out there in electronic form it seems like the tide has shifted, but I still buy cookbooks for general cooking stuff, and still find myself printing out recipes that I find online (like an old person!) so that I can actually use them in a kitchen environment.
Technical books, reference books, textbooks seem so incredibly natural for an interactive format, but I'm not aware of anyone that has cracked this. The closest metaphor I've found is having tabs in a browser, so I can store a limited history of my exploration of a topic, but it rapidly becomes an unnavigable mess.