IBM researchers have simulated 'half' a mouse brain on a Blue Gene L supercomputer. For comparison, a real mouse brain has 8 million neurons with 8,000 synapses each. The simulation had 8 million artificial neurons with 6,300 virtual synapses each. It was only run for 10 seconds at one-tenth the speed of real-life...which equates to one full mouse second.
Quite a virtualization overhead if you ask me.