If you go to the Google AdWords Certification Program Learning Center you will now see that Google is offering 4 exams, not one exam - to take and to earn your certification with Google AdWords. The exams include:
- Google Advertising Fundamentals Exam
- Search Advertising Advanced Exam
- Display Advertising Advanced Exam
- Reporting & Analysis Advanced Exam
There is actually a whole grid of courses you can review before taking the exams. I am not sure if you can actually take all four exams yet, but it seems like you will be able to do so soon.
Forum discussion at WebmasterWorld.