Author and thinker Seth Godin had a recent post on ad clicks: the bottom line is that all ad clicks come from 16% of internet users, and most come from 4%.

What does this matter? If you’re optimizing your ads for clicks, you are overfitting your ads to appeal to 16% of the internet and ignoring the other 84%. It’s something to keep in mind when viewing your click performance stats, and one of the reasons we sell advertising based on time, instead of clicks or displays.