Facebook's biggest problem

What if Facebook's biggest challenge isn't financial at all? What if is actually its users?

At last official count, Facebook had 901 million active users, and was slowly but surely marching towards 1 billion. Although the company will undoubtedly tout that important milestone, lurking in the shadows will be one major issue all social networks have had to contend with: fickle users. Facebook is so aware of the issue that it made it a top risk factor in its S-1 Registration Statement filed with the Securities and Exchange Commission earlier this year. "A number of other social networking companies that achieved early popularity have since seen their active user bases or levels of engagement decline, in some cases precipitously," the company wrote. "There is no guarantee that we will not experience a similar erosion of our active user base or engagement levels."