The following returns undefined in Internet Explorer 9 (IE8 works fine) using jQuery 1.8+ but works in jQuery 1.7.

<style type="text/css">
	div{
		background-color:#F4F4F4;
		background:-webkit-gradient(linear,0% 100%,0% 0,from(#FFFFFF),to(#ECECEC));
		background:-webkit-linear-gradient(top,#FFFFFF,#ECECEC);
		background:-moz-linear-gradient(top,#FFFFFF,#ECECEC);
		-ms-filter:"progid:DXImageTransform.Microsoft.gradient(startColorstr=#FFFFFF, endColorstr=#ECECEC)";background:-ms-linear-gradient(top,#FFFFFF,#ECECEC);background:-o-linear-gradient(top,#FFFFFF,#ECECEC);
		height: 400px;
	}
</style>

<script type="text/javascript">
	$(function(){
		alert($('div').css('filter'));
	});
</script>