Okay- I have no idea how this works. I can't find a Cashback notice on the Commit to buy page of any item I am looking for so it is proably just hit or miss. Hope you make out better than me!
Here's how to save up to 40% with a coupon + Microsoft Cashback:
1. Search for an item on www.live.com.
2. Click the sponsored ad with the Microsoft cashback symbol You'll be taken to eBay.com.
3. Make sure the item is Buy It Now and the seller accepts PayPal. If the item is eligible,you'll see a cashback notice on the "commit to buy" page.
4. Enter code: CSHOPEBAY2008. Pay with PayPal before midnight PT on Dec 1, 2008.