I just thought I'd remind everyone that I'm also one of the bloggers over at the MCLC TechTalk blog. I've put up a few posts lately, so you should check it out!
Like Kottke, I've also been obsessing over this optical illusion. Which way does the dancer spin for you? Does she switch? Can you TRIGGER a switch? My initial reaction is always clockwise, but I can make her switch pretty regularly.