I read this thread yesterday and it seemed like a good deal:
35% cash back from eBay purchase using Microsoft Live Search *No selling!* - Page 109 - SlickDeals.net Forums
Freaking 35% back from Microsoft! The catch is, it only works on certain items, but it does cover some large purchases like PS3s, Xbox 360s, etc. It will only work on buy-it-now listings however. I would read the thread I linked to above for comments from others who have tried this.
Comments from people who did this deal and examples of deals:
Ebay Buyers - Possible 35% CASHBACK from Microsoft - [H]ard|Forum
Here are the terms and conditions for the offer from MS:
Live Search cashback - Live Search
Just wanted to pass this along since I know some people use ebay alot. This has the potential to save hundreds of dollars.