Also on these boards
How Do Google AdWords Work? - Pay the most money, and you can get your text-only ad to be number one on Google, right? The Google AdWords system is far more complicated than that. A good “Quality Score” gives an edge to advertisers, even if they aren’t the highest bidder. “Ad Extensions” mean that ads can show pictures, maps, ratings and more.
The Google AdWords Landscape (Infographic) - SEOmoz
Who Buys All Those Google Ads? An Infographic Breakdown ~ credits:http://www.wired.com/epicenter/2012/01/google-ad-buyers-infographic/
Google #Adwords Pie: Which Industries Use Google Adwords. Top 100 Advertisers with Monthly Ad Volume by Industry. This chart is from September 2009. Although the percentages will be different today, it's still a good representation of which industries partake and which do not.