One third of all items posted to Facebook are from mobile devices

"Some stats have been published, by researchers and the company themselves, about mobile usage of Facebook. But to content creators, one of the most important uses of the social network is when users create posts, sometimes posting original content, often sharing articles and media found elsewhere on the web. I was unable to find much data about how much of this activity occurs via mobile devices, so I decided to research my own.
I used a random sample set of more than 70,000 Facebook public posts (those from users with open privacy settings). The data includes status updates, videos, links and photos. 32.69% of those posts were created from mobile devices. The mobile Facebook website, m.facebook.com lead mobile usage with more than 18% of posts created through it."

Source:  Research by Dan Zarrella, posted onto his blog, 9th May 2011