Varnish is a reverse-proxy cache that allows a site with a heavy backend (such as a Drupal site) and mostly consistent content to handle very high traffic load.

We’re steadily getting closer to a vision of the semantic web – and it’s being driven by Facebook through their Open Graph Protocol.

Technical article (Planet Drupal)

I guess a lot of people that have to deal with integrating videos on a website for iPhone and iPad, will  - at some point - run into the problem that some videos simply won't play.