Facebook has updated its Android app. It's a pretty significant update because it adds Facebook Chat functionality, which was previously unavailable, and for some people a big part of Facebook use.
The update also adds push notifications to Android devices running version 2.2 or above. Chat doesn't require this high of a version, however.
In the summer, Facebook reportedly had 150 million mobile users. That number has likely grown significantly since then. Android has continued to make strides as well.
Mobile has been a significant part of Facebook for some time now, but that is likely to continue exponentially as more people buy smartphones (not to mention tablets), and as Facebook Places continues to find users and use cases.
Facebook recently attached more privacy controls to the mobile experience. This should please a growing mobile user base, considering all the privacy concerns around the social network that have come out throughout the year.
Facebook CEO Mark Zuckerberg was named Time's Person of the Year for 2010 for the impact that Facebook has had on society. It will be interesting to see what kind of impact Facebook continues to make in 2011 on an increasingly mobile web.