I don't understand this? If you 'block' an IP address from coming to your website - that's not going to stop that IP address clicking on your advertisements on Overture's partner sites (Yahoo! / MSN etc).
So the blocked IP guy could still happily click on your advert on Yahoo!/ MSN or whatever website - the click instigates the charge - they'd just never actually 'get' to your website (because you blocked them by IP).
Wouldn't the click still be charged?
Am I missing something?