This is a helpful book, particularly for anyone fairly new to the internet. It lets you bypass the trawling that usually needs to be done and get straight to sites which have the information you need, or at least links to it.
Categories are fairly well laid out and the most important sites are covered in each. While it is by no means a comprehensive guide, it is growing year on year, and often the listed sites will be more comprehensive portals to the info you're after.
While it is a fairly general book covering the wide scope of the whole internet, it's probably worth the low asking price if you do occasionally venture from one particular subject type which you already know the relevant sites for.