I wonder if IE6 users are more prone to click on ads anyway. Overall, this is an interesting idea. If you implement it, follow up in a couple months with what the effects are. My company has thousands of pageviews a day, with about 25% being IE6. I would love to push this idea internally because A) it makes the marketing dept happier if we make more money and B) it makes me and the other front-end engineer happy.