You might have downloaded Flickr and Twitter last night, but your Vita's social (networking) life was still missing one crucial component as of yesterday: a dedicated Facebook app. Well, now that's been taken care of, as you can head to the PlayStation Store and download the app.
The official PlayStation Facebook page notes that the app is "only" 12 megabytes, so bear that in mind when considering how best to fill your valuable, valuable memory card.