I mentioned this in my news story today about Microsoft's recent online ad ventures, but thought you might be interested in a bit more information. FIrst, here's the official line from Microsoft:

At advance08, Microsoft’s annual advertising customer event, Bill Gates announced the launch of an innovative new search business model, Live Search cashback. With the new experience, Microsoft will offer ad-funded cash rebates to customers who find and purchase their favorite products through Microsoft Live Search cashback. Barnes & Noble.com, Sears and Zappos.com, three of the 700 participating merchants, joined Bill on-stage announcing their support for Live Search cashback.

Additionally, Microsoft launched Live Search Farecast, incorporating technology acquired through Microsoft’s April acquisition of award-winning travel Web site Farecast. Live Search Farecast helps you find the lowest airfares by predicting when is the best time to buy, so you can time your purchase for the greatest discount. Microsoft will explore the possibility of also incorporating a cash rebate option for travel services booked and purchased through Live Search Farecast.

I've actually used Farecast in the past and it doesn't appear that they've change the site much beyond that small new LIVE header that showed up first on the Live.com search results pages. Indeed, there's no integration with Windows Live ID yet, which I assume is part of the plan going forward.