Ad units are like water: they’ll eventually flow into every nook and cranny of your screen real estate. We’ve all witnessed the generations of efforts — some successful, some not — to find new and more prominent places to stick just one more ad. We’ve seen pop-ups, and pop-unders. We’ve seen banners, towers, skyscrapers, super-skyscrapers, thumbnails and every possible size you can imagine. We’ve even seen the cursor itself used as ad-space (remember
