Facebook has 819 million monthly mobile users, and makes 41% of its ad revenue from mobile

"Second Quarter 2013 Operational Highlights
Daily active users (DAUs) were 699 million on average for June 2013, an increase of 27% year-over-year.
Monthly active users (MAUs) were 1.15 billion as of June 30, 2013, an increase of 21% year-over-year.
Mobile MAUs were 819 million as of June 30, 2013, an increase of 51% year-over-year.  Mobile DAUs were 469 million on average for June 2013.
Recent Business Highlights
Surpassed 1 million active advertisers on Facebook, driven by significant growth in local businesses.
Introduced video for Instagram and saw 5 million videos uploaded in the first 24 hours.
Facebook for Every Phone has now passed 100 million monthly active users.  In just two years, Facebook for Every Phone has successfully put Facebook into the hands of millions of people around the world with limited access to the Internet, giving them the power to connect and share.
Launched products including Verified Pages, hashtags and embedded posts to help people on Facebook connect with their friends about what's taking place all over the world.
Announced that there have now been over 100,000 apps built on Parse, a cloud-based platform that provides scalable cross-platform services and tools for developers to enable them to build apps that span mobile platforms and devices.
Facebook's data center in Lulea, Sweden, began serving live user traffic around the world using Facebook's Open Compute Project designs and renewable energy.
Second Quarter 2013 Financial Highlights
Revenue — Revenue for the second quarter of 2013 totaled $1.81 billion, an increase of 53%, compared with $1.18 billion in the second quarter of 2012.
Revenue from advertising was $1.60 billion, representing 88% of total revenue and a 61% increase from the same quarter last year.
Mobile advertising revenue represented approximately 41% of advertising revenue for the second quarter of 2013.
Payments and other fees revenue was $214 million for the second quarter of 2013, an increase of 11% from the same quarter last year."

Source:  Facebook Investor Relations, 24th July 2013
Previous results:  751m monthly mobile users, 30% of revenue from mobile