Now kids, remember that the acid test isn't exactly a measuring line - it's more a test of the browser's ability to jumps through some (pretty arbitrary) hoops. Of course, a big score is nice, but somewhere above 90 is pretty good enough. As for IE, i'm not surprised, those people don't care about any standards anyway. They're proud their latest IE8 is able to get 32!
@squirreluk, most streams should work, as long as they're a common enough format, not some exotic stuff. How much traffic you use up by doing this depends on what quality the stream has and how it's compressed. But if you can find wi-fi, it's free!