Official site is here: https://www.paypal-promo.com/holiday/slider/index.html

Terms are here: https://www.paypal-promo.com/holiday/terms.html

I just used this on Overstock - the order total had to be over $100 though, but I don't think there is a minimum at the other sites.

The 20% off comes as cash back from Paypal sometime next month.

can we use merchant coupons also...

I don't see why not. There's no special codes with the paypal promotion, so you should be able to use any coupon codes you might have in addition to getting the 20% back.

Don't bother with the NewEgg one. It expired yesterday afternoon. Evidently, PayPal gives them a set amount of money to fund these promotions. Once the money is used up, that's it. It didn't take long at NewEgg especially when everyone was ordering PS3's and 360's. They were maxing their $50 cash back with one purchase.

Overstock pulled the plug on this promotion last Thursday.
And now it looks like B&N are also no longer participating.
Man, that was fast...

Wow, I was only able to get in one small order at B&N which will get me back about $6.xx via PayPal. Oh well.

I just received my cash back from Paypal yesterday - keep an eye out if you got in on this. Thanks to the original poster - I saved around $37 at B&N.

Yeah, I got $30 back from Overstock and about $7 back from BN.com before the deal disappeared. Nice job on Paypal's part keeping up their end of the bargain.