Gardner's work debunking pseudo-science of all kinds is even more relevant today than it was when it was written nearly 50 years ago. Although it has been 30 years since I read it, I can still remember many of the funnier highlights of the book.
For example, some of his revelations on crackpot scientists are truly hilarious. In his chapter on health and health food faddists he discusses Gaylord Hauser, who was a famous name in the area long before people like Adele Davis, Ewel Gibbons, and so on.
Gardner mentions Hauser's famous theory that acidosis of the blood is responsible for just about all health ills, and recommended fasting to counteract it. Unfortunately, anyone even slightly familiar with human physiology will tell you that fasting actually causes acidosis, a little fact apparently Hauser overlooked. Another great theory killed by a nasty little fact, I guess.
Then there is the chapter, "Down with Einstein," where crackpots par excellence try to prove they are smarter than Einstein. One guy by the name of Gillette (no relation to the razor concern) says of Einstein, "As a physicist, Einstein is not a bad violinist," and insists his "Back-screwing Theory of Gravitation" is far superior to Einstein's. According to Gillette, "...gravity is naught but the kicked-back nut of the back-screwing bolt of gravitation." As you can see, Einstein is not the only genius physicist out there with a good theory or two.
The one person Gardner actually seems to like in this book is Charles Fort, the journalist who himself reported on much of the pseudo-science of his day. Fort was a diligent and witty writer in the area who seems to have been fascinated by things like UFOs, the paranormal, strange phenomena, and bizarre scientific theories, and who appeared content to write about and document it all without really believing any of it himself. The Fortean Society he founded to carry on his work is still around today.
I could go on and on about all the funny things in this book, but I will stop here and let you discover them for yourself if I've managed to peak your interest. This is one of the most entertaining books of science writing ever published, and really qualifies as a classic in its own right that is still as relevant as the day it was published 50 years ago.