You can use this on ebay for anything that has a "Buy it now". After you click on the ebay link, you just do a search for whatever you are looking for...like say Gucci.certain things. you'll go to bing, search for "wii" or another one of the key searches, then you'll see a few bing cashback logos which should stipulate how much you'll be getting (10% for now). Click through those links and search for what you want on ebay.
you should be able to see in your search results what is cashback approved (I think it's most things that are "buy it now", you probably also have to pay with paypal). Ebay and Bing CB are actually pretty well integrated so you'll see the amounts you'll be getting back on your ebay screen.