I did see a pretty significant slowdown on IE7 (XP service pack 3) in the Crystal Galaxy demo in the section where there's a wall down the center of the screen

I did see a pretty significant slowdown on IE7 (XP service pack 3) in the Crystal Galaxy demo in the section where there's a wall down the center of the screen and a big mass of the "bubbles" both above and below. By the end of that, it's really chugging. Firefox 3.5.4 is really smooth, though, and IE7 is surprisingly smooth even then.