Intellectual fads are interesting because, unlike the fad for Paris Hilton adopted by the lumpenproletariate (which my friend Pete Sattler is mocking daily at his new blog PromoteThisBlog), these are false or useless ideas adopted by very smart and educated people. A lot of times, this manifests itself in people overinterpreting the usefulness of a theory, or applying it somewhere else. For example, supposedly a pretentious older woman asked Einstein for his opinion on what his Theory of Relativity implied about ethics. He replied, "none that I can think of".
Claude Shannon wrote a mathematical definition of information based on the concept of entropy in thermodynamics, and this proved very useful for coding, data compression, encryption, and other aspects of information processing. But that's it. Some people thought it would be useful in linguistics, psychology, economics, biology, and even the arts. But Shannon stated to science writer John Horgan, "Somehow people think it can tell you things about meaning, but it can't and wasn't intended to".
In the 1960's, Rene Thom developed a mathematical theory that captured phase shifts, applicable to chrysalis, earthquakes and societal collapse. His 1972 book, Structural Stability and Morphogenesis, was reviewed by the Times of London as follows: "it is impossible to give a brief description of the impact of this book. In one sense the only book with which it can be compared is Newton's Principia. Both lay out a new conceptual framework for the understanding of nature, and equally both go on to unbounded speculation."[Nov 30, 1973]
You don't hear much about that anymore.