Gary Price over at the Search Engine Watch Blog writes an entry named A Week After Launch Yahoo! Search Developer Network Lists More than 20 Applications, where he lists several tools that were already developed using the new Yahoo! API.
Here is one such tool that you guys might find useful.
Yahoo Link Pop Checker. Of course, you must download it and install it on your machine, because Yahoo! limits queries by IP address as opposed to by key. So if it was hosted, it simply would not work for you.
I am actually bugging some of my Yahoo! contacts to hook me up with a large volume of queries, so I can build you guys a free nice fancy tool. Wish me luck.