Hi,
I think the following would be a good improvement on Promo Codes
1. Make Shipping Null i.e. Free Shipping
2. Promo Codes by Shop Category (i.e. Select a specific category or categories to which the code can be applied)
3. Specific Product (an extension of the previous - the ability to identify a particular product within the Promo Code)
There are other things as well (such as selecting User Groups or individual users) but these are probably a long way off

Cheers,
Dirty Dave