Restaurants not in my area, maybe I tweet "When are we gonna get a <popular restaurant> I keep hearing so much about on <local radio station>?". Not an immediate return on investment but maybe a hint at where to build next. Medicines, or anything else that may not be for me? I know a bunch of other people that talk all day about things they need and problems they have. If I hear about a potential solution for them, I'm probably going to mention it next time I see them, maybe even shoot them a quick text right now.
My experience with targeted ads is either way off base or suggesting something I don't need because I literally _just_ bought it. But mostly I don't experience them because they're so easy to block. Then they don't even get the potential benefits of word of mouth.
As far as fraud, the roll of an online advertising company should be to ensure both parties are holding up their end of the deal, ensuring links go where they are supposed to and sites are presenting ads as agreed. That can be done with code the ad companies write for the advertiser and content providers to run on their own servers during the agreement. Pawning that off on the user machine doesn't solve the fraud issue, but apparently advertisers are convinced it does, for now. It does get you tracking, but only as long as users put up with it. It's lazy and, hopefully, it won't be a profitable solution much longer.