The geniuses at Google, the world's most arrogantly clever ad sellers, have announced plans to target ads to Internet users based on their "interests." You can opt out — but there's a catch.

Susan Wojcicki, the Google vice president who's also the sister-in-law of cofounder Sergey Brin, announced that Google would start tracking the websites people visit, wherever Google serves ads — which is something like 90 percent of the Internet worldwide. Google will then assign "interests" to those users based on their online browsing, and serve up ads accordingly.

As Google product manager Shuman Ghosemajumder explains in the clip above, Google is making it easy to modify the interest information Google stores. You can opt out, but then the "ads will be less relevant to you." (The horror!) What Ghosemajumder, Wojcicki and the rest of the Googlers are really hoping you'll do is add or subtract interests to the list rather than opt out — and thereby give Google even more information about you.

If anyone bothers, that is. In a survey of Internet users from March 2008, 91 percent of respondents said they would make use of privacy tools if better ones were available. But they are — Google's hardly a pioneer. Yahoo announced a similar opt-out scheme last year, and less than 1 percent of users bothered to visit the ad-preferences page.

The truth is that privacy is a problem everyone likes to talk about in public, and no one actually bothers with in private. It's a handy bugaboo for activist groups, a reliable topic for pundits and journalists. A trendy thing, perhaps, to whine about in online message boards.

But is it relevant to our online lives today? In an age of oversharing, when we update Facebook with every emotion and Twitter every Web page we come across, when we blog, blog, blog it all, is Google really the biggest threat — or is it us?

And if it's us, where's the preference setting to turn it off?