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GitHub User: dbackeus
In effect the example you give of styling based on an id in body is pretty much the most extreme way of breaking the pattern (one thing I've noticed out of experience is that the "further away" the container definition is the more complicated it becomes to make sense of the css logic).
Theres a good video outlining some of the reasons (basically CSS anti patterns) behind OOCSS here:
Great overview of Rails 3.1!
Would prefer Flash being the default and HTML5 video being the fallback for playback though. Fullscreen is kind of crippled in HTML5 (possible with Chromes fullscreen mode activated but noticed that screen dimming and screensaver will still activate).