I took the Google Adwords Professional exam today and passed with 95%. My impression of the exam is that is was relatively straight forward. The biggest challenge in most cases is interpreting what the question is asking. The best source to prepare for the test is the Learning Centre, but make sure you are using the most updated version. I noticed there was some out of date links. It is in theory an "open book" exam. This is not to say that you shouldn't study. My plan of attack was to go through each question as quickly as possible without referring to any material. Then, time permitting, go through each question checking if the the answers I provided were the best. I ended up finishing the questions quite quickly which meant I had plenty of time to check and double check my answers. The fact that I got a few questions wrong would probably due to ambiguous or vague questions. If you have any questions regarding the exam format, please feel free to ask away.
Congratulations on passing! I have this in my to-do list although the $1,000 spend is a barrier right now.