Rating: 

Easy to carry, easy to use; absolutely invaluable.

Lots of things could make this book more comprehensive, but would also make it heavier.

A companion website with additional resources might be cool. This could just be a compilation of external resources, maybe just some well organized links, etc. On the other hand, it might just be redundant since there are already a billion great websites for these sorts of things. Yeah, my bad; I can't say it's not a perfect book!