Facebook recently announced that it now has over 2 billion monthly users. This makes its “population” larger than that of China, the US, Mexico and Japan combined. Its popularity, and with it the influence it has in society, is beyond dispute. But for many the experience of actually using the site fluctuates somewhere between the addictive and the annoying. Our new research shows that the reason for this is very simple. It’s all to do with other people, and how we feel about them.