From the Google Blog:
"Despite all the development we've done for our AdWords program, much more remains to be built. Fortunately there's no shortage of good ideas outside the Googleplex -- our community of users is amazingly expert and innovative and knows exactly what features they want. Many successful companies fall prey to the NIH ('Not Invented Here') syndrome, but as hard as we try, not every talented developer is working at Google. Which is why we've just announced the arrival of the AdWords API beta.
The AdWords API beta program is an open invitation to developers to explore new concepts (and then write great software) for managing Google AdWords advertising campaigns. Large advertisers can use it for their complex ad management needs, like tying product margins to optimized keyword bids. Third parties can use the API to build new interfaces to manage their client accounts. Best of all, an API enables the creation of all sorts of unanticipated ideas. In our experience, it's better to wear 'Not Invented Here' as a badge of honor than as a chip on your shoulder. Come sign up for a developer token and show us what we've been missing. "