Alternating widget styles

I just upgraded to 3.3.1 and my widget style filter is broken. Is there a new way to inject the filter?

add_filter('widget_content', 'make_alternating_widget_styles');
function make_alternating_widget_styles($content='')
{ global $make_alt_ws, $make_alt_ws2;

	if(preg_match('/(sb2 )/', $content)){
		$make_alt_ws=($make_alt_ws=="style_a")?"style_b":"style_a";
		return preg_replace('/(class="widget )/', "$1 widget_${make_alt_ws} ", $content);
	} else {
		$make_alt_ws2=($make_alt_ws2=="style_a")?"style_b":"style_a";
		return preg_replace('/(class="widget )/', "$1 widget_${make_alt_ws2} ", $content);
	}

}