This is how google describes the new service:
“Interest-based ads: Show ads based on user interest categories. Visitation information from my sites may be used to help create interest categories.”
As a webmaster this is a good thing. Google ads have just became smarter, which means more clicks and obviously more income.
On the other hand, as an internet user, your browsing habits will be recorded. So if you look up a new game on Google then visit a couple of websites talking about it, you should expect to see ads about this game (or other games) for the rest of the day (hopefully). It is as if somewhere on the internet your name is linked to this game forever.
I tried to corner the new interest-based advertising by visiting multiple websites about a certain movie, then opening a couple of unrelated websites and another movies review website, but I did not succeed. Maybe because interest-based advertising is not activated yet or I am just doing it the wrong way.
For your info I kept interest-based advertising activated (it is on by default). But if I notice a any movement against it I’ll deactivate it immediately.