Technologies which did not live up to the hype

There are many, many false technological alleys which continue to be pimped as things worth investing time and money into.

• Automotive Gas Turbines:
  In the 1960s, several car manufacturers made gas turbines. The batmobile, for example. Turbines were supposed to be “jet age” machines of the future. You could get more fuel efficiency and energy per cubic meter out of the things, plus they were simpler in design (in theory, only one moving part), and easier to cool (they basically cool themselves). Unfortunately, gas turbines are lousy at acceleration in stop and go traffic. You might some day have one in your laptop though.
  
• Disco Space Colonies:
  Back in the 1970s, when America had just been exposed to its first real energy crisis, a fellow by the name of Gerald Kitchen O’Neill came up with the marvelous scheme of blasting enormous chunks of glass and metal into space (presumably not…