4. Mobile Messaging

At the last board meeting, Erskine asked if I thought things were going too well and what our biggest risks are. My answer to this is that mobile messaging is the next biggest consumer risk and opportunity. Mobile messaging means people sending private messages -- like text messages -- rather than posting things more broadly.

The basic math here is that people share more things with smaller groups than they share with all of their friends at once. On mobile, your SMS, email or other primary messaging app is generally the most important and most used app on your phone.

Therefore, the biggest competitive vector for us is for some company to build out a messaging app for communicating with small groups of people, and then transforming that into a broader social network. Companies like Line and Kakao in Korea and Tencent in China are running this exact strategy and it's working reasonably well. They haven't expanded outside of Asia yet, but this is a big risk for us.

In addition to being a risk, this is also a big opportunity for us. If we execute well here, there's an opportunity for us to significantly increase the volume of sharing and communication on Facebook. For the past 18 months, our mobile message sends has more than doubled every six months.