Want to know which technology scares me the most ? AI combined with nanotechnology. Here's an interview with professor Vernor Vinge, a pioneer in artificial intelligence, who's claiming we'll be getting near the Technological Singularity near 2020, which indicates the point where man-made machines will be more intelligent than man.
Bill Joy, the former Sun executive, warned in 2000 with his Why the future doesn't need us, an essay with some somber thoughts about how our most powerful 21st-century technologies - robotics, genetic engineering, and nanotech - are threatening to make humans an endangered species.