Don't know if anybody's using the MS Live Cashback thing, but it looks like they're offering 30% cashback on eBay auctions today. I just snagged two copies of CTDS (one for me, one as a Christmas present) and I'm getting $23 back. (Plus $8 off upfront from a coupon eBay sent me.)
Not sure what else they're offering deals on, but they've got NewEgg listed as a partner -- looks like cashback from stuff there is only a few percent, not 30%, but still, a few bucks is nice.
I'm a little late to the party on this one as it's over at midnight Pacific, but yeah, if you hit up
live.com, do a search for something you're looking for, and then click on the eBay sponsored link, apparently that's 30% off. (Make sure it's Buy it Now, the seller accepts PayPal, and there's an MS Cashback symbol on the "commit to buy" page. And you'll have to be signed up for an MS Cashback account before you do it.)
In summary: for $23, Microsoft got me to use their search engine instead of Google's.
...now I'll go check if there's anything else on my shopping list that this deal applies to.