#box1
{
	background:green;
	width:150px;
	height:auto;
	border:5px solid red;
	padding:5px;
	position:absolute;
	top:1em;
}

#box2
{
	background:green;
	width:150px;
	height:auto;
	border:5px solid red;
	padding:5px;
	position:relative;
	top:4em;
}

In standards-mode browsers, the two boxes should be the same width, but in IE7 the first box is shorter - as though it were in quirks-mode.

{fixed in beta 2}