i donno...
i've been using photoshop since version 1.0.
i really digged deep with the version 3.0... ('cause i was running a digital photo studio at the time)
in my case... i'd say that there's nothing like just getting your hands dirty.
no one book is going to completely teach all functions and tools of Adobe Photoshop.
so depending on your level of knowledge... pick your books accordingly.