Google AdSense has really given small publishers a method of earning a nice supplemental (sometimes full) income doing what they love. But some see the AdSense checks as extra spending money and some don't. A thread at WebmasterWorld asks What are the special things you do with your Adsense money?
At first I was going to skip over this thread and not report on it but then I thought again. Remember that the Yahoo! Publisher Network allows you to perform a balance transfer from your YPN account to your Yahoo! Search Marketing (YSM) account. The only requirement is that you register your YPN account under the same username as your YSM account. Screen image for you below on the interface, and see questions 35 & 36 in the Yahoo! Publisher Network Beta Help.
So for only one member (currently out of 11 posts) in the thread to say that he puts the money back into Google AdWords, it encourages me to post this. I am not sure the intent of launching AdSense outside of increase AdWords inventory and making more money. But with YPN, they are definitely looking for YPN publishers to transfer that money right back into their YSM accounts.