I think it's a good idea and one that could work well. I have been reaping the benfits of your hard work for over a year, and this sounds like a great way to keep the site going strong. One question, though - how will you, or will you, regulate the ad space? Will you give advertisers the freedom to do what they want with their space, or will you limit them in any way to ensure that they keep the site's design usable and clean?