From the Facebook PMD newsletter:

We reached 1 Billion Users – 600 million of them use Facebook on mobile.

We created our very first TV ad to mark the milestone. [Side note: View the video below! - LA.]

You should check out the One Billion Fact Sheet. e.g. “219 billion photos have been uploaded since launch.”

Also, Cleverbug.com made a very cool video about it.

1 Billion users = 1 Billion consumers, and as you know this is a huge opportunity for marketers.

Invoke’s note: Need we say more?