bumpski - 1:52 pm on Dec 17, 2010 (gmt 0)
count for less than 0.1%
But the real question is how many of those visitors actually have the Toolbar PageRank feature on. Not many I'll bet. So why not try it? The thought being webmasters may be the source of there own poor performance data.
I don't doubt that image ads do boost earnings on very high traffic sites.
Regarding a performance fix. Until about 2006 I successfully displayed targeted adsense ads inside IFrames, truly boosting site performance. This is allowed by the TOS. Google broke this functionality, I believe, at the time they added "section targeting". At that time targeting in an Iframe went away big time. Truly a shame. In fact at that time the Adsense Advisor dujour contacted me with Sticky mail hoping to work on the IFrame problem. I shouldn't have turned him down, but I was losing money!
Adsense could generate the ads on their servers and serve them in an IFrame (like Amazon) and use an ajax transaction to verify the referrer string fed to the Iframe. But it seems Google wants to use as much of the visitor's CPU and bandwidth as possible thereby off loading their servers.
Have you ever looked at the code on their home page? It used to be so pristine; not compliant, but pristine! Now it's huge mess!
Part of the Adsense code structure is obviously there and mandated as an attempt to thwart any tricks one might try to deceive the code with alternative, hidden content. I get the impression that even premium Adsense users take a performance hit, which is truly surprising.