stuartmcdonald - 6:56 am on Apr 25, 2005 (gmt 0)

"When site-targeted and keyword-targeted ads both are eligible for display in a given position, they compete equally for ranking. The AdWords ranking system takes into account the max CPM prices of all site-targeted ads, compares them to the combined cost-per-click prices and clickthrough rate of keyword-targeted ads, and then displays the highest-ranked ads. "

From here: [google.com ]

That reads like it is across the site rather than per page. The advertiser sets their maximum CPM -- not their minimum (that is apparently set by Google at $2). If I'm reading that correctly then it seems would encourage publishers to not keep adverts on pages that are dragging down the across the site CPM.