I first learned of this from Richard Rutter, but the idea apparently comes from Dustin Diaz. April 05 has been designated as the “CSS Naked Day” - where sites are stripped of all stylesheet rules for the day. As Richard points out, April 05 lasts for about 48 hours if you consider the entire planet, with datelines and such.
If you really dig around my site, you will see the occasional flash of inline or embedded CSS, because I only disabled the external styles. They will have to remain as embarrassing monuments to presentational markup.