According to Google PR, there's been a "650% increase in queries from June to July across the country" for various versions of the term. They wouldn't tell us how much money automakers and dealers have spent on searches, but a search reveals Toyota, GM, Hyundai, Mazda and other automakers are buying up ad space. Additionally, local dealerships are also doing targeted searches that lead to special sales pages.
All of this demonstrates an awareness by some automakers of the power of search for driving traffic to their sites and foot traffic to their stores. All these ads appear to correspond the release of the Cash For Clunkers rules. You can see some of the ads popping up on our browsers below.