Cengage recently announced that 250+ titles will be available as online books through CafeScribe. Krugman is available for $58.67.
It seems that the goal is to allow highlighting and annotation, and sharing of these notes among a community of readers. So far 11 folks have purchased Krugman, and one person has added two brief notes.
I'm skeptical. CafeScribe requires installing the MyScribe application. This required a 56.8 Mbyte download for Macintosh. The website and application appear both slow and clunky. The application crashed the first time I launched it, and the website gave we 404 errors.
Although it's promised on the homepage, I wasn't able to find a full demo book to download. At best I found a two page document, so it's hard to tell what full texts will look like.