[jeffreymcmanus]

If nobody sees your ad, it costs you nothing. Whether the ad is effective or not is a function of whether you can convert a clickthrough.

[huhtenberg]

AdBlock in Chrome prevents ad images from being displayed, but they are still downloaded. This is different from FF where ads are blocked at the downloading stage. In other words the impression counter can easily go up without ads being actually seen.

[jeffreymcmanus]

That is why CPC advertising exists.