I noticed that a project I've been working on ran very slowly in IE7 and IE8 compared to FF3 and Chrome. Took me a while to track it down but it seems to be wmode related. The file in question had its wmode set to "transparent" in the containing HTML document. I did a bit of digging around and stumbled across Justin Everett-Churchs WMode Woes. He knocked up a quick demo page that shows that with wmode set to "transparent" or "opaque" any setInterval calls are slowed down to the framerate. This means my fancy scrolling system stutters like a sod since it isn't being updated fast enough. Luckily for me I can turn it off on this project. I still love the wmode parameter but now I know its limitations. It'll still work a treat on non time sensitive animations. I'm not sure if the setInterval/wmode pitfall applies to ActionScript 3s Timer class, I'll have to test that on the next AS3 project I'm on.