Default report is available in report -> sales -> coupons.

And with script you can find used coupan count and customer details very easily :

    $coupon = Mage::getModel('salesrule/coupon/usage');
    $coupon->load('code', 'coupon_id');
    if($coupon->getId()) {
        $timesUsed = $coupon->getTimesUsed();
        $customer = $coupon->getCustomerId();
        echo $timesUsed;
        echo $customer;
    }