The worst offender I've seen so far was on Hulu I think. You could either watch the 1 or 2 minute advertisement, or type the company's slogan into a text box. That really weirded me out...
Ticketmaster just changed their captchas to this format as well, you enter a captcha like "Who's coming with me" while viewing an ad about their social features. Until a few months ago it was a normal, unrelated captcha.