As you know, Yahoo! partnered with eBay and PayPal to create Yahoo Checkout. By signing up with Yahoo! PayPal Checkout, you can get a shopping cart icon in your Yahoo! Search Marketing ads.
This is basically how Google Checkout worked when it first started. Then I looked into if there were any benefits to the Google Checkout icon on your AdWords campaigns. In short, some people saw an increase in traffic, with a static level on conversions; which means they saw more sales.
My question is now, does Yahoo Checkout have the same impact? Increase in traffic, same level of conversions, but an increase in sales due to the traffic increase?
There is a forum thread at WebmasterWorld waiting to be filled up with feedback from Yahoo! Search Marketing advertisers who use Yahoo Checkout.