user-counter

// Add Shortcode
function custom_shortcode() {

	// Code
$result = count_users();
echo 'There are ', $result['total_users'], ' total users';
foreach($result['avail_roles'] as $role => $count)
    echo ', ', $count, ' are ', $role, 's';
echo '.';
}
add_shortcode( '', 'custom_shortcode' );