In Our Magnificent Bastard Tongue, John McWhorter presents the case that the Celts were the reason for the introduction of the "meaningless 'do'" in the English language, and presents other similar implicit influences that have no recorded evolution in formal language. Counterarguments cite that since the evolution wasn't written down, it didn't happen that way.
Twitter may be the first opportunity for us to actually observe a recorded evolution of language as it actually occurs. Twitter is an extension of text messaging, which is a proxy for the bleeding edge evolution of spoken language. With the Library of Congress archiving tweets, we may have the first official and publicly accessible record of the nuances of change in language.
Before Twitter, most written communication occurred, minimally, in the writer's best dressed understanding of the language. Some email may be a little bit different, but emails are lost to abandonment of accounts and servers, and still follow etiquette more closely than a medium purposely restricted to 140 characters. I thought about its impact of recording speech usage when I mimicked nonstandard use of "because" and "why is" in my social media posts. Regardless of whether our own language use immediately evolves, we are reflecting the "misuse" of language more than ever before, and possibly as a larger sample of overall recording of language.
Why not radio and television? Because access to publishing on TV and radio is restricted to a relatively elite class of publishers, just as scribes, as the only literate class, controlled the language that was written. Art and music is more representative, but is still restricted by the boundaries of was is "good" even if a popularity formula is the judge of "good and proper" rather than grammar rules.
Facebook and other social media have similar impact, but Facebook has privacy controls that limit its visibility and other social media (LinkedIn, Google+, blogging) are prone to professional scrutiny and editing due to longer form.