Pretty amazing. Make sure you check out the videos. Here's one of them:
http://download.current-biology.com/supplementarydata/curbio/17/23/r1004/DC1/mmc7.mpg

Quoted: Clearly, the chimps have the number thing down. So the researchers added an element of spatial memory, as you can see in this movie. After the first digit is touched by the test subject, the remaining numbers are obscured. As that video makes clear, this didn't slow down the chimp significantly. As a final test (shown here), the chimp is only afforded a brief glimpse of the numbers; his success rate didn't budge significantly. In contrast, humans (specifically college students) had a hard time with this test, barely outperforming the mother and losing badly to the young chimp.