In response to Florida Governor Rick Scott attacking Florida universities for graduating too many psychology majors (among other disciplines), a group of department chairs put out a report explaining and defending the discipline. Toward the end they list some famous psychology majors, and among them is Mark Zuckerberg.
Here’s Zuckerberg in the Deseret News:
“All of these problems at the end of the day are human problems,” he said. “I think that that’s one of the core insights that we try to apply to developing Facebook. What [people are] really interested in is what’s going on with the people they care about. It’s all about giving people the tools and controls that they need to be comfortable sharing the information that they want. If you do that, you create a very valuable service. It’s as much psychology and sociology as it is technology.”
And it’s not just talk — he’s hiring psychology PhDs (including a University of Oregon graduate).
See also here (psych major stuff starts around 1:00; gets especially interesting around 2:50).