I confirmed this too with Urchin statistics since it only shows 15 referers from google being half of them from direct searches.
So, this leads me to think that MyDoom Virus attacking Google is also affecting AdWords in the way that it might count the click but then fail before redirecting the user to the advertised site.
If this is the case Google is charging for non delivered hits.
Could anyone confirm their adwords stats against your own stats?