Comment 80 for bug 217580

the best example:
http://stinkt.kicks-ass.org/1b6cc1af2e8437646c9b7422d78e6eb3/slidecast%20-%20studio%20-%20vertical-view.html
(this is a static copy of the site)

just try scrolling with you mousewheele up and down very fast. Then you can see that the page is still scrolling seconds after you stoped to scroll. Often firefox also gets gray because compiz thinks that it is not responding any more.