Facebook's mobile apps are frequently among the most popular downloads in the Android Market and Apple App Store, but just how many people are tapping into the social network from their smartphones and tablets?
Facebook's Wednesday IPO filing revealed that the company had more than 425 million monthly active mobile users during December 2011, or about half of its worldwide user base. An active mobile user is defined as someone who logged in to Facebook - via an app or the mobile site - from their mobile gadgets.
The newly public social network attributed part of that growth, particular in the U.S., to the increasing adoption of smartphones, as well as improvements to the various Facebook apps.
"For example, we improved our product offering on feature phones following our acquisition of Snaptu in April 2011 and we launched the Facebook app for the iPad in October 2011," the company said in a filing with the Securities and Exchange Commission.
Boosting that mobile usage will be "critical to help us maintain and grow our user base and engagement over the long term," Facebook said. "We expect consumers around the world will continue to increase the amount of time they spend and the information they share and consume through mobile devices."
But while that 425 million number might be impressive, it's not making Facebook any money at this point.
"We currently do not show ads or directly generate any meaningful revenue from users accessing Facebook through our mobile products, but we believe that we may have potential future monetization opportunities such as the inclusion of sponsored stories in users' mobile News Feeds."
Facebook said last month that sponsored stories would be coming to the desktop newsfeeds sometime this year.
"Our revenue may be negatively affected unless and until we include ads or sponsored stories on our mobile apps and mobile Web site," Facebook said.
Meanwhile, "there is no guarantee that popular mobile devices will continue to feature Facebook, or that mobile device users will continue to use Facebook rather than competing products," the company said. "We are dependent on the interoperability of Facebook with popular mobile operating systems that we do not control, such as Android and iOS, and any changes in such systems that degrade our products' functionality or give preferential treatment to competitive products could adversely affect Facebook usage on mobile devices."
There's no indication that this is a looming problem, but something Facebook must highlight in these types of documents, which are geared toward investors.
For more, see Facebook By the Numbers: Steady Growth, Big Profits and What Facebook Fears, as well as the Facebook history slideshow below.