Many who turn to these resources are desperate. They're sick and they're looking for answers. Obviously, the inherent danger is the reliability of the information they find. Ferguson's book is the first I'm aware of that is written by a physician. He steers you to the best of the best, providing a page or two of narrative explaining the best features of each site.
Many descriptions also give examples of actual postings.
Interspersed throughout is general medical information written for the lay person. There's also technical information for using the Internet, and Ferguson proves his expertise here as well. A big problem for many Internet users is that they tend to wander. I do myself. I set out to find something specific, get distracted, and hours later still haven't retrieved what I set out to find.