Sorting posts using dates coming from Custom Fields

I am trying to sort a post loop using custom fields using the Y-m-d setup. So I want a post using 2010-12-22 to come before an 2011-01-06. But using my query below I dont get that functionality. Can someone help me?

$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;

        $args = array(
		'post_type' => array('news'),
		'posts_per_page' => 10,
		'meta_key' => 'cft_startdate',
		'meta_compare' => '>=',
		'meta_value' => date("Y-m-d"),
		'order_by' => 'meta_value',
		'order' => 'ASC',
		'paged' => $paged
	);
	$query = query_posts($args);