Consider the case of clicking a link in an email someone sent me for a joke. My google account thereafter managed to associate me with bestality [1]. Fun eh?
Now ironically, over a year later, I was still getting rather awful targeted Google Ads advertising and SPAM to a supposedly unrelated email account (on Windows Live with no associated Google account). The persistent google cookie from hell dragged that information and my three static IP addresses across multiple sites and managed to basically bombard me with shit.
Something somewhere managed to make the associations and send directed advertising. They had me profiled.
That in my mind is unacceptable, which is why I don't want to sign up for another profiling account.
It's not paranoia or conspiracy crap - it's fact.
Regarding usenet: there's no reliable way to profile people on it due to its architecture.
[1] I accept some responsibility for clicking a link in an email of course.