http://www.nytimes.com/2009/07/25/nyregion/25bear.html?pagewanted=1&_r=1 (NYT -- registration may be required)
Basically, they have these food containers that require you to press a button, turn it half way, press another button, and turn it the rest of the way. At least one bear (named 'yellow-yellow') figured out how to open it.
For what it's worth, some humans can't figure it out. I especially liked this comment somebody made, "Turns out there is considerable overlap between the stupidest human and the smartest bear."
