We all know the types of ads that Google is saying they are going to block here - and good riddance. I really wish I knew of some study - but, my personal theory is that roughly 100% of those ads are trying to sell some scam or download some virus. It's really hard to imagine a legitimate company that sends users ads with fake close buttons, pop ups, redirects, fake mouse pointers, etc and after the user trudges through all of that they end up at a page advertising 10% of garden shears at the local hardware store.
Yes - Google sells ads. Yes - Google, apparently, now blocks ads. Yes - that sounds troubling. And it sure will be troubling is if it turns out that they are blocking legitimate Ad Words competitors. But, these aren't really ads by any reasonable definition: these are overwhelmingly anti-user malware scam garbage. In my opinion, it's pretty troubling if a super profitable company like Google has the ability to make such a user-positive change and _doesn't_ do so.
Maybe its step 1 down a slippery slope to actual bad behavior. But, let's get worked up about that when there is some actual evidence of bad behavior - it's not like there won't be plenty of people interested in trying to keep tabs on what Google is doing here.