If I'm not mistake google doesn't get paid for ads unless you click on them. In other words google doesn't charge Ads customers for impressions, only clicks.
I was discussing regular web links. I think Adsense is still PPC, which is a bad deal considering it may not result in a conversion. I’ve only used it when they send me $100 free credits. It tilted in no sales. I actually sold a book in my website last through MySpace, so I’m probably not an expert on any of this.