I am not certain if the KW's get ranked. However, depending on what you type into the google search engine, will often produce all sources including social media. I would be interested to see if it was for the KW's, or based upon the phrase or even the persons name.
Often, I will see public messages that a person types into FB, if I am searching the name. I tested this for some KWs and did not seem to get the same results for that same person coming from FB.
I will be keeping my eye on this question, as this could be a good method that might have just gotten discovered!! Thanks Info Guy for bringing this topic up.
Hope my answer helps this question