“As I outlined above, Safari adopted a “cloud library” model rather than downloadable ebooks as its fundamental design metaphor. I thought it might be worthwhile to understand how we arrived at that decision, as well as some of the other lessons we’ve learned over what is now 22 years of ebook publishing experience. (O’Reilly published its first ebook, Unix in a Nutshell for Hypercard, back in 1987!) With that, a few reflections on lessons learned”
http://radar.oreilly.com/2009/10/safari-books-online-60-a-cloud.html