While it doesn't seem like a big deal, the rise of the mobile site and the accompanying apps could lead to a drop in revenue for Facebook at a time when investors are going to want to see growth in the company to justify its stock price. On its regular site, Facebook shows 4 to 7 ads per page. But on the mobile site and on the apps, there are only a few ads shown daily. This means that the more people that switch to using the social network from their smartphone, the lower the amount of ad revenue that Facebook will collect. In fact, in its prospectus sent to potential investors in Facebook's stock, the company noted that the higher the number of mobile users, the worst its business is doing.
Facebook members on the go can do everything from their handset that they could do with the regular site. 78 million Americans age 18 or older use the mobile Facebook site and they spend 7.3 hours per month using it. 160 million Americans access the social network from its regular web page, using it for an average 6,5 hours per month.
Since Facebook CEO Mark Zuckerberg didn't want the mobile site to be full of banner ads that take up most of the screen, Facebook decided to offer Sponsored Stories. These are stories that might have appeared on your news feed, but is more prominently listed in exchange for advertising dollars. These started showing up in March, but the number of these stories has been kept down so as not to annoy mobile Facebook users. The problem here is that this lowers the revenue that the company so badly needs now that it has Wall Street as its master.
source: comScore via TechCrunch