It struck a lot of Webmasters as ironic that Google made page speed a rank signal when AdSense scripts was one of the factors slowing sites down. According to Google, it slowed publisher sites by about 12%.
Gone are those days. Google developers improved the show_ads.js JavaScript needed by AdSense publishers and sped up delivery of ads. Google claims the changes will speed up publisher sites by a half second or more. After running Page Speed and YSlow tests, we’ve seen a noticeable improvement in scores. Publishers don’t have to upload new code since the change is automatic. Right now, the changes are working with Chrome, Firefox, and Internet Explorer 8, with more browsers and versions included soon.
If you need to block the new ad version, set “google_enable_async = false” for each ad slot.
Tags: AdSense, Google, page speed
The main reason I started the SEO Revolution was out of frustration. Frustration at all of the lies and misconceptions that are posted in forums, given as advice in teleconferences, and even taught in live workshops. "So why didn't all of this work?" " Why wasn't my site successful?" " Why am I still stuck in a rut?" 
I have noticed a dramatic increase in page speed for those pages displaying Adsense ads. I do believe Google has improved the (js) file to load ads much faster.