In IE8 hit F12, set the browser mode to IE8 and the document mode to IE8 also.
Then go to any web page with an button with an image overlaid on it, and notice that when you click down / mouse down on it, the button image will move left -1px and top -1px.
This affects everything from the search button on the bing.com homepage (although it defaults to ie7 document mode), to the select and add to cart buttons on the apple store. It looks really bad and only seems to happen in IE8 when the above modes are set.