Always nice to see something free from Apple, and the timing couldn't be better. The iBooks version of the iPhone User Guide for iOS 6 is available on the iBookstore.
Apple isn't much on paper manuals these days; most Apple products come with a thin little guide, so many users get their tips from websites like TUAW and others.
This Apple e-book is quite complete, with chapters explaining all the new features in iOS 6. I found the chapter on Siri and changes in the camera app most helpful. The book is illustrated, and every bit as good as something you'd buy online or at a book store.
This is a good idea, but it's certainly not being trumpeted by Apple; you just kind of have to know it's there. That's what we're here for, so get over to the iTunes and download it. Apple is also offering free user guides for the iPhone, the iPad, and iOS 5.1 if you didn't upgrade.
There's a few screen grabs in the gallery. The book can only be viewed on an iOS device using the iBooks app.