There were/are two different cashback programs that have been running and will end soon.
The eBay cashback program:
eBay was offering 5% cashback on qualifying purchases - but as I understand the eBay cashback program, you had to receive an invitation from eBay via your eBay user name in order to participate in eBay's cashback program. They offered 5% cashback on qualified purchases and the eBay cashback program ends on August 13, 2008 around midnight. BTW, there was a 7 to 10 day period where eBay doubled their cashback from 5% to 10%.
The cashback accrues until around midnight 8/13/2008. You can redeem the eBay cashback accrued from August 21st to September 21st. You can request vouchers in differing amounts to use or if you don't specify, then eBay will only allow you to use your cashback in one lump sum on one purchase on eBay - in an auction that takes PayPal as payment. If your purchase was less than the cashback amount you had accrued, then you lose the difference. If your single purchase is more than your cashback amount accrued, then they will apply your total eBay cashback towards the purchase and you would have to pay the difference.
The Microsoft Live Search cash back program can be read about at the following link (it's too long to explain here).
Live Search Cashback Program Linkhttp://search.live.com/cashback/
The Live Search cashback program is still running and you can still sign up for it. When the Live Search cashback program began, they were allowing 35% cashback on qualified purchases (read their rules) - up to a single cashback of $250 maximum. You could do three transactions total and no single cashback earned could exceed $250 - however, you could make smaller purchases (but only three to earn the cashback).
They aren't offering 35% cashback now, however, depending on the item you searched for via Live Search, some discounts at certain stores are up to 25%. The discount varies by store and by the item you put in to do the Live Search on. They also offer specials every now and then - like right now, if you go through Magazine.com (via the Live Search link), you can get 70% cashback from Live Search on your entire purchase.
I think that the Live Search cashback could be collected either 60 days or 90 days after your qualifying purchase. I know my first Live Cash back redemption I will receive on 8/17/08. The other two will be available on their individual purchase anniversary dates. Live Search gives you the choice of having a check mailed to you for each redemption - or you may elect to have the cash put into your PayPal account. They don't care which (unlike eBay).
There are a lot of threads on these cashback programs, but I thought I'd share what I know about the two programs. Anyone can sign up for the Live Search cashback program, however, you have to set up a Live Search cashback email address and sign on to Live Search in order to qualify for the Live Search cashback deals and you can also see what discounts you can get at different stores (jncluding eBay) on the Live Search.com site. I hope this helps.
JR