Does anyone here on the forum use this approach, and more importantly, what kind of customer do you get? Frankly when I read this kind of site myself, I just laugh at them - I figure there is some fat, bookish nerd ripping off photos of girls, boats, cars, what-have-you, creating the site. In any case I'll bet there is a certain group of people who actually do sign up just because of the "challenge" that is hidden in the text. Thinking back to Joe Vitale's "Hypnotic Writing" I would bet this addresses a certain niche: that of the person who cannot say no to a dare who is also into internet marketing.
Anyway, I would be interesting in your thoughts on this topic, especially if you have tried it!