Some early examples:
AI has always made sweeping promises about how close we are to developing intelligent machines. (See: Minsky, Ray Kurzweil.) But the problems in AI are difficult to solve, and following initial excitement about the field, it faced what's known as the "AI Winter," when funding for its development was slashed.
AI has had far more successes in recent decades -- the self-driving car, Siri, and Watson being three well-known examples. But debates remain about the shape AI should take. (Google's Peter Norvig and MIT's Noam Chomsky have sparred over this.)
Speaking of Norvig and self-driving cars... Artificial Intelligence and MOOCs: The founders of the xMOOC startups all have AI backgrounds: Stanford professors Andrew Ng, Daphne Koller, and Sebastian Thrun and MIT professor Anant Agarwal. (And yet, they can't even write a good MOOC recommendation engine.)
So will robots replace teachers? Are the robots coming for all our jobs?