coupon is working good for me. The discount will only show on the "Review Order" page. Look under payment method it should have the following listed (for example, a 10% off coupon):

Subtotal: $51.97
Coupon Discount: 'MYCOUPONCODE': -$5.20
Total: $46.77

You should also have the capability of adding in a coupon code to an existing order in your order list.

Now about whether its working or not...do you have:
1. A coupon code listed that is working with a set value and a valid date under your Coupons admin page (admin/store/customers/coupon)

2. which ubercart version are you running? 7b or bazaar? I have 7b that it is working on right now.

3. What coupon values do you have? Here's mine: I have put in 10.00 and chose "Percentage" as the Discount Value Type. Coupon is set to Active, with expiration date of 12/30/2007, 0.00 for minimum order amount and 0 for maximum number of redemptions. Both wholesale and retail are allowed to use coupon and I have not selected any specific user under "Allowed Users" so anyone should be able to use it.

let me know if you make some progress.
-Aaron