Agreed, and soon they will be using Bing in their serps. Will they still be a search player? I think so.
When we look back to the Google and Ink days Yahoo! has more or less a customer. They paid for the service provided by the provider. How with a strategic agreement in place Yahoo can free up their resources and concentrate on ad sales. Not haveing the massive outlay of running their own search engine but still displaying results will probably help yahoo's bottom line.