Did you notice mute this ad a new cross sign at corner of adsense ads. when you click on that cross you get notice 'ad muted' .
Yes, The "Mute this add" button will tell google you are not interested in that type of advertisement, for example if it displayed an ad for the new call of duty game, you mute it, and will not see an ad related to call of duty again. In theory at least.
This is a cool feature, but I will not suggest to use this feature, as this will only strengthen Google to determine your likings and make a DB on that. instead if you don't like any ad just ignore it. If you not at all like to see any ads use Ad Block Plus.
I think this is a pretty cool feature. I, for one, like the idea of Google being able to serve me the most relevant advertising it can. And as others start using this feature, it should theoretically improve click-through rates (by serving more relevant ads) and ultimately improve earnings for us Adsense publishers.
It's good that such a feature exists, as far as I know it's been around for years, well done mr google.