FB is a much larger company than the average IPO. Larger companies often grow slower as they dominate their markets. With 900 million users, it would seem that the developed countries are fairly saturated and won't see much growth in the user base.

I would be interested to see some projections for FB costs over the next five years. They no longer have the lure of pre-IPO equity to attract new employees. They might have to pay higher salaries instead. Many insiders will be cashing out in the coming months and moving on, so I would guess that FB salary costs are going to climb significantly.