I've used bing cashback several times. It'll save you a ton of money. You have to wait like 60 days to get your money though, and then pay you via amazon payments. Which you can then either transfer to a checking account or use as an instant amazon giftcard. I saved about $200 on an ring for my fiancee using it.
Using bing shouldn't affect applecare. When you register for applecare, they don't care where you got your mac, or where you bought applecare.
I would only buy a mac from an authorized reseller, but thats just me