Machines are doubling in raw computational speed, but have yet to show signs of intelligence. In fact, it's pretty obvious by now that intelligence is not merely a function of raw computational speed; there's some other, as yet unknown, factor which is necessary. Once this factor is identified and can be artificially created, then yes, machines will quickly outpace humanity... but what is known about this factor is that it is very, very hard to identify.

Though it seems unlikely that AI will fail to be invented over the next century, it has nonetheless non-negligible probability.