"With the Yahoo! PayPal Checkout Program, a blue shopping cart icon appears next to your ad in Yahoo! search results. This can help your ad stand out, and let customers know you offer PayPal Express Checkout, from the brand known for security."
PayPal offers free processing until the end of the year, like Google. But there's more:
"The ability to quickly locate PayPal merchants will save you some time because the PayPal checkout system remembers all of your personal information, providing you (and me) with the convenience of a single username and password, as well as a consolidated look at your transaction history so you can view all of your purchases and track each items' shipping progress."
This seems pretty familiar, isn't it? Here's a fragment from a Google post written after Google Checkout's launch, in June last year:
"One cool feature of Google Checkout is that you can buy from stores with a single Google login – no more entering the same info each time you buy, and no more having to remember different usernames and passwords for each store. To help you find places to shop, you'll see a little icon on the Google.com ads of stores offering Google Checkout. It's an easy way to identify fast, secure places to shop when you search. And after you've placed your order, Google Checkout provides a purchase history where you can track your orders and shipping information in one place."
This is only about ads, Google and Yahoo have many common advertisers and there are some merchants who use both PayPal and Google Checkout. Google forgot about users' choices to promote Google Checkout, while Yahoo is always on Google's footsteps and replicates every new feature or product.