I certainly share your sentiment in that I don't like my "info" being shared with the likes of advertisers, but I do think you might be a tad misinformed, and someone I hope will correct me if I'm wrong. I think that the only way your 'info' would be shared, is if you actually clicked on an ad, and decided to participate in an advertiser's campaign, such as a contest to win a prize. But even then, I think that the only thing being shared (I'm not positive about this though) is your name and zip code.
I haven't read about iAd in depth, and am getting this info based off of Steve's keynote address, where he demonstrates iAd and shows the contest which Nissan is hosting.
I'm also with you in that I don't want to see ugly adds on my screen, which might detract from the apps natural graphic flow, but you might be able to 'x' them out and close them, not sure about that either.
There is one thing for sure though, in a world of smart phones, you'll be really hard pressed to find an OS which hasn't opened its self up to adverts, and I'd personally rather deal with the way Apple is handling the way they're presented than any other manufacturer right now. Ads on the Android system might actually pose a threat to the user, considering the nature of the OS they're running on, whereas with Apple's iOS 4, you know that everything is being scrutinized in order that it benefits the advertiser AND the user.
In a perfect world, we wouldn't need to deal with advertisements, but the fact is that the world where tech goods are manufactured, bought and sold, are totally consumerist, and that falls in line with making as much money as possible. Apple's simply making the most out of it for everyone involved, in the best way they know how. And I'm really certain that they wouldn't put the millions of users they have at risk in terms of having their personal information in dangerous hands.
If you're very concerned, it's pretty easy to find Steve Job's email address. Why don't you shoot him an e mail with your concerns and ask some questions? I bet that he, or someone representing him directly will answer you sincerely. If you ask specific questions, they have to be transparent about the answers, since they're in teh public eye and have a lot to lose if they're hit with a law suit involving a case such as misuse of private/personal information.
Doug