If you are looking for a book you could do a lot worse than Adobe Photoshop CS4 for Photographers (ISBN-10: 02405212500). It's currently available from our affiliate store
Amazon for about £20/$33. It covers everything from Bridge, Adobe Camera Raw and Photoshop itself through to the niceties of colour management and printing and comes with a DVD which includes photos you can practice on as well as some instructional videos. At 704 pages it covers a lot but even the author admits that a further book, Adobe Photoshop CS4 for Photographers: The Ultimate Workshop (ISBN-10: 0240811186), is needed for the really advanced stuff.
Hey, thanks. I've just noticed that The Ultimate Workshop was published a few days ago so I've just ordered it.