I would buy other photography related book instead. Generally I find them more "long lasting"...
i actually prefer just buying picture books.. these will always be relevant because.. a good picture remains good forever.
whereas knowledge garnered, you should be internalising it, after which, you don't need the book anymore!
of course, for more advanced things like photoshoppery and advanced lighting techniques, you might want to refer back.. but for basic photography, compositional guides, etc.. i don't really see a purpose.
I've seen places selling guide books on Canon EOS 500D/40D/50D etc...is it useful? How is it compare with instruction manual? Have anyone seen books on 7D?
shoot alone is not sufficient. good books are equilly important.
In fact my 1st criteria of a camera model or brand is how intuitive their body is. Back in manual days, we dun really need instructions manual....and even up till today DSLR era, I dun have to refer to a manual to use 1. The buttons and how the menu are arranged should be simple enough for you to navigate not referring to the manual at all. If you need to find out what does a particular function does, then you probably just need to read on more on basic digital photography terms.
I would say yes, these are certainly the books to buy. They are, in a way, timeless.If the book is on how to take better photos with techniques, methods and photos to illustrate, then would be useful. If it is another book on how to use your camera, then you are better off using the thing than reading about it.