If you see an increase in CTR: Lets hope that if you see an increase in CTR it doesn't lead to lost rankings in Google. It's possible that if this adsense change significantly improves your ad CTR then your visitor metrics will suffer and bounce rate will increase. When that happens it's possible that Google, in turn, lowers the perceived value of your site. For that reason I am extremely unhappy with the less than 24 hour official notice before this was activated, it's just been bumped to the top of the list of things to monitor. Rankings are a fickle thing.
I'm somewhat worried about colorful favicons on dark unit backgrounds since these jump out at you significantly. That and we all know that the adsense team and search team do not work closely together(emails saying add more units leading to lost rankings etc).
Interestingly it looks like the spammers have already caught on. I'm seeing some extremely well recognized logos next to totally unheard of domains.
Actually Google is using the favicon it has associated with the site so if the spam site was using another companies favicon it will display it in advertising. I have a feeling that favicons beside ads will suddenly become a hot topic on a legal front, companies like Amazon, eBay and Microsoft do not appreciate anyone confusing possible customers using their highly copyright logos.
Expect the lawsuits to begin soon enough because of this seemingly minor Google change. Companies take their ad spend and copyrights extremely seriously. I'd expect Google to be inundated with a rash of takedown requests before it escalates. Did they prepare for it?