I've long pointed out that human brains are far more complex than computers. However given Moore's law it seems likely that somewhere in the 2015-2030 range (depending on how one defines the complexity of a neuron), computers will be a match for human brains in complexity. At some point after that happens I expect human level AI to appear.
The growing power of statistical techniques for previously impossible tasks like translation and answering Jeopardy questions (see the computer IBM is putting together) suggests that once the requisite CPU power is available, it won't take long for computers to match humans on a wide variety of cognitive tasks. Once you hook together the right selection of abilities, I expect something that looks suspiciously like original thought to emerge.