Fixes salesrule times_used data update bug introduced in Magento CE 1.8 and EE 1.13 Salesrules with zero sum discount amounts (such as salesrules created for free shipping) will not have their times_used data updated.

salesrulebugfix.diff

Index: app/code/core/Mage/SalesRule/Model/Observer.php
===================================================================
--- app/code/core/Mage/SalesRule/Model/Observer.php  (revision 146067)
+++ app/code/core/Mage/SalesRule/Model/Observer.php	(working copy)
@@ -90,7 +90,6 @@
         $customerId = $order->getCustomerId();
 
         // use each rule (and apply to customer, if applicable)
-        if ($order->getDiscountAmount() != 0) {
             foreach ($ruleIds as $ruleId) {
                 if (!$ruleId) {
                     continue;
@@ -129,7 +128,6 @@
                     $couponUsage->updateCustomerCouponTimesUsed($customerId, $coupon->getId());
                 }
             }
-        }
     }
 
     /**

The reason for this "if ..." was to properly calculate usage of coupons during multi-address checkout. Without it, the usage of a coupon with fixed discount for the whole cart will be counted not once, but equal to "number of addresses".

David, I understand the case you're trying to fix. However, it would be great, if you can write down the exact step-by-step scenario, expected and actual result - so I can provide it to our QA and devs. Also, as you have access to EE, then you can contact support to ask for a patch - this will be a fast solution for you.

Scenario:
A salesrule is created that requires a coupon code, and is configured to only be used once. The salesrule has either a 0% discount, or a $0 fixed amount discount, and allows for free shipping. The rule doesn't have any conditions or item conditions. A user uses the coupon and places the order.

Expected Result:
The coupon code should no longer be valid after use

Actual Result:
The coupon is still usable since the times_used attribute is not updated.

Relevant code:
~ Line 93 of class Mage_SalesRule_Model_Observer in method sales_order_afterPlace

Thanks for the insight Andrey!