By FAR the slowest thing to my site is Adsense. About three quarters of the page load time is loading the two ad networks I use - because they load scripts, which load other scripts, which load images... a waterfall view shows it very clearly. Even Google's own Page Speed confirms the problem.
The page load time showed in webmaster tools suggests that this is what Google is measuring.
So, is my site being classified as slow because of adsense, and am I likely to be losing traffic because of that?