A Google AdWords Help thread is a myth busting thread on the topic of blacklisting AdWords campaigns. Two Google representations confirm that Google will not blacklist or ban AdWords campaigns due to have a low or poor quality score.
One advertiser asked, "Can your account be "blacklisted" in regards to the Quality Score of the Landing Page?"
This might be considered a popular myth. Why? Well, if a campaign or keyword has a low quality score, it may feel like you have been blacklisted. But your ads won't show or your bids will skyrocket not due to being blacklisted but more due to having a poor quality score.
Both AdWords representatives gives more advice on how to improve your quality score in the thread.
Forum discussion at Google AdWords Help.