I just notivced that one of the revolving ads on my site is little more than Adwords in a vertical banner. I know the ad is from Google. But what is pretty cool, is that SOMEHOW (maybe with it's giant cache!) google tailors each adword ad on my site to be relevant to the words on that page. (That is, EACH ad is dynamically generated based on the content of the page it is called from!)
Just as, if you were to buy adwords for Widgets and your ad show on a search for Widgets... if my page is strong on the keyword Widget, you ad is on my site.
As an aside, I INSTANTLY blocked that ad... why would I want my competition on my site like that?