At a Gaming Event in Palo Alto today, Facebook CEO Mark Zuckerberg revealed that games are one of the primary reasons some people visit Facebook, confirming that 40% of its userbase is using the site for social gaming. The top ten games on Facebook have more than 12 million users each.

But Zuckerberg says it’s complicated, “While they’re in the top five things that people like, they’re also in the top five things that people hate.”

Read more in Jason Kindcaid’s liveblog from the event.