In a previous article I covered how CakePHP would potentially be moving to using sphinx for the 2.0 documentation. Myself and some of the other CakePHP developers have been working on this option, and seeing if it has any legs. Turns out that sphinx is actually a pretty great tool.
In the release announcement for 1.3.7, it was tentatively announced that CakePHP would be moving its documentation over to ReST, Git and sphinx. Having documentation in a git repo, and using sphinx to generate documentation has a few nice wins, that would be difficult to achieve with the current book application.