HALF MOON BAY, Calif. – If you’re reading this post, you probably have a Facebook account and you might have encountered a phenomenon on Facebook known as friend deflation.

Thanks to the popularity of Facebook, some users are getting lots of “friend requests”  – including some from people they don’t consider friends. Fortune Brainstorm organizer David Kirkpatrick held a fireside chat with Facebook’s chief operating officer Sheryl Sandberg, who was asked how users can overcome the social pressures to accept such requests. Sandberg suggested users create different lists for different friends.

“As we’ve opened up the site from college students to the public, people have different definitions of the word friend. Anyone can create different friend lists, whether it’s your personal friends or professional friends, that gives people different access [to your profile],” she said. She added that a Facebook user can choose to ignore a friend request and the rejected person won’t be notified.

An audience member yelled out that Sandberg should make a feature to “acquaintenance” someone.

Asked if she thought Twitter, a site that allows users to write brief updates of their status, was the next hot company, Sandberg responded by talking about Facebook. “I don’t know if I’m an expert on Twitter, but I will say that there is a lot of conversation about things that are short. Is there value in throwing a sheep or poking someone? If you think about it as entertainment or communication, I think that’s really valuable,” she said.

Sandberg’s interview, packed with several hundred atteendees, was the most popular session of the day. Longtime tech expert Esther Dyson asked the audience how many had Facebook profiles, and all but roughly 20 hands went up.