The numbers I've seen suggest that it's total 'processing power' is only on the order of a few hundred teraflops - and we already have plenty of clusters bigger than that. I know that floating point operations per second is a crappy metric but consider that a neuron can only spike about 100 times per second (i.e., the brain runs at 100 Hz) - even billions of neurons put together just aren't that powerful in terms of hardware.
Software, not hardware, is already the limiting reagent to 'smart' computers.
Everyone says 'massive parallelism' is the answer. But once transistor density plateaus the only way to add more cores (i.e., add more parallelism) will be to make CPUs physically bigger (or make each core 'weaker'). Making each core 'weaker' adds very little net benefit (2 * 100 = 20 * 10) and having physically larger CPUs isn't really practical beyond a point ...