The top systems today are approximately at the same capacity as a human brain.
Brain neurons perform an operation that's similar to a dot product. Their operation can be simulated by a weight for each dendrite that's multiplied by that dendrite's input.
In rough order of magnitude, a human brain has a hundred billion neurons, or 1e11 in standard computer language notation. Each neuron has an average of one thousand inputs, 1e3, and performs a hundred operations per second. That is 1e11 * 1e3 * 1e2 = 1e16 flops, or 10,000 teraflops.
According to Top500, the highest powered computer system in November 2012 had a capacity of 17,590 teraflops.
This doesn't mean it has the same ability as a human brain, because there's also the software involved. There is a project, sponsored by Google, that tries to implement a computer system operating close to what the human brain does.
When they tested that system presenting to it one million random screenshots from Youtube videos, the system learned all by itself to recognize objects that appeared on those videos, like human faces and cats.
There's a good technical tutorial on this system at the Stanford university site, and a more basic explanation can be found in several popular articles if you google for "deep learning".