Of all these scenarios people have mentioned, I haven't heard any talk, even joking, about a "Robots take over the world" type of thing.
That said, the idea of machines developing a form of consciousness, while remote, still strikes me as a plausible idea -- especially as the years go by. This speaks directly to Moore's law, which says that computing power *doubles* every 2 years.
Day 1, you buy a calculator.
2 years later, your calculator has enough computer power to be a word processor.
2 years later, your word processor can do everything a home pc can do.
2 years later, your home pc is talking to the world through an interconnected network, complete with satellites.
2 years later, your pc is accomplishing computations once performed by supercomputers, the kind of crap that puts rockets into space and decodes the human genome.
2 years from now, where will your supercomputer be?
It is easy to say that a computer will never approximate human life -- that we have a soul, free will, destiny, any of these things that make us different. But could there come a point where the computing power is enough to simulate synapses in your brain?
Watching this video, there are definitely dark undertones... either by the prospect of machines fighting humans, or of what will become of war when machines fight machines, controlled by humans.
I fear the desensitization of a person ordering a machine to kill, from thousands of miles away, as the target screams, bleeds, and dies with the same vigor as ever.
This guy is a great speaker, and if you have the time, I'd be interested to know what you folks think of where we are heading.
PW Singer on military robots and the future of war | Video on TED.com 
