Apparently, www.naughtyamerica.com is a online sex(uality?) site that is promoting its services through a game called "Naughty American History." In this game for every American history question you answer correctly the 'professor' removes one item of clothing.
I am embarassed to say that I only got my professor down to being shirtless, before I stumbled on a 'Whig' question.
I can't imagine such incentives ever catching on with either current history students or professors. In all my years of taking history classes, with the vast majority of my professors, I would more likely study to make sure they kept their clothes on - rather than take them off.