A new wave of AdWords Quality Score  drops is troubling advertisers again. A thread on the AdWords help boards suggests that it started last Friday, just before the weekend. A Google employee has confirmed  that fixing the problem is now a priority for Google's engineers.
I used the Excel sheet from WordStream's Quality Score Toolkit  to analyze the changes that occurred in one of our accounts. Below is the account's usual Quality Score distribution:
The red bars show how often a Quality Score occurs in the account. The green line is an average Quality Score distribution according to WordStream's worksheet. The graph below shows the same account today:
As you can see, the drops are significant. On average, Quality Score dropped almost two points.
Still, I don't think advertisers should be worried. A similar problem occurred about a month ago, when lots of keywords displayed worse than usual Quality Scores. Back then it was just a reporting issue: The numbers you could see on the AdWords interface were simply wrong. The real Quality Scores Google uses to calculate ad position and CPC were not affected.
It seems like this time it's the same problem with displaying correct numbers again. As far as I can see, none of our accounts has any kind of problem with clicks, impressions or ad positions. On Google, our ads appear just as usual. So don't worry. Just wait for Google to fix the issue.