This nifty timewaster's been around since early October; someone just brought it to my attention, so now I'll bring it to yours. By bookmarking this link, you can play Asteroids on any page. Watch me shoot up Crecente's bio!
Put the link in your browser bar, as I have, and then when you click on it, it starts the script on whatever page you are currently viewing. Get around the page with standard controls (space: fire, up is thrust, rotate left, rotate right) and have fun shooting up stories and comments that displease you.
Thanks Eric S., Whizkid103 and others, for the tip. Wish I'd seen this sooner.