At www.optimine.com we are doing some interesting stuff to address the abysmal CTR of display ads.

The key is to measure the effect that your display ads are having on your paid search ads, ie measure the "brand effect" impact on purchase decisions.

The direct effect of banners ads is negligible, but that is missing the point. Nobody clicks on a Coca-Cola TV ad, but they aren't going to stop TV ads anytime soon.