Offhand, I can think of six excellent reasons to buy what's available free online. I can scan through five or ten book pages while a single Web page oozes through my 21.6K phone line onto my screen. Books are easier on the eyeballs than tiny flashes of electronic light flaring at an astonishingly high pulsation rate from a sheet of coated glass. Browsing through a book, I can pick up any number of interesting items I would never have thought to look for, while I tend to use electronic directories for pointed searches. Perhaps it has something to do with our slightly diminished ability to pay attention to other things when online.
Nothing can replace the plain physical satisfaction of owning a book.
Harley Hahn's books on the Internet are authoritative, original, light-hearted yet accurate, and best of all, interesting. Here you'll find descriptions of Web sites and Usenet newsgroups on every subject imaginable. For comprehensive information presented entertainingly, you can't beat Harley Hahn. This one's topic and subtopic organization makes it hard to find things. The massive index helps, but often merely mirrors the order of the listings.