Scrap that, I was checking the actual post list for the meta instead of the post itself.
Try this instead:
add_action( 'wpsp_before_content','wpsp_add_custom_meta' );
function wpsp_add_custom_meta()
{
$meta = get_post_meta( get_the_ID(), '_your_custom_meta_key', true );
if ( isset( $meta ) && '' !== $meta )
echo $meta;
}