Numerous educational technologists and social media advocates have linked to this short video titled The Machine is Us/ing Us.
It is the work of Assistant Professor of Cultural Anthropology Michael Wesch, from Kansas State University. The video summarises the revolution that is the read/write web, including rss feeds, blogs and wikis.
It'll take just five minutes of your time.
UPDATE The original video links pointed to a beta version. I've updated this post to point to the final version.