At Fortune’s Brainstorm Tech conference, a keynote Q&A with Sheryl Sandberg, among many issues, talked about leadership and exec changes at Facebook.

Adam D’angelo, former CTO: “He has left to come back couple of times…we would love to have him back. There is no specific underlying story behind the few execs leaving our company. Leadership at the company: Zuckerburg’s focus is around product and engineering. I am leading on the business side.”

Mobile: “The iPhone application is doing very well for us. As long as we are monetizing on the site, we are fine on the mobile side, since we are pushing people from mobile to online.”

Twitter: “If you think about it is as communication and entertainment, we think people are communicating in short bursts, and it’s very valuable.”