As you can see, many of these features take advantage of the online medium in ways that aren’t possible with standalone ebooks. To be sure, there are times you want your own offline copy, and in Safari Books Online, you can indeed download books or chapters for offline use. But especially given the rise of the smartphone as an access device, the times when we are truly "offline" are becoming few and far between. The vision with which we started Safari, that of always-on access to a library of technical content, not just to individual ebooks, is now within reach. Safari Books Online can be used on a desktop or laptop computer or in the browser on a mobile phone. Everything is always in sync because your library is in the cloud. An ebook cloud works the same way the web itself works. It provides ubiquitous access and shared experience.More here from this useful post. The Safari Books Online homepage can be found here. Subscription details here. Another example of how to monetise intellectual property not by charging per title but by charging per volume: ie not for what we're looking to read but rather for how much.
An overarching access versus the purchase of specific content is the battleground the future clearly entails. For now, I think I far prefer O'Reilly's cloud to what, in retrospect, may soon begin to appear to be the Kindle's hurried rewriting of an inappropriately bricks and mortar economics.