Leosghost - 6:49 pm on Sep 3, 2012 (gmt 0)
Advertisers only pay if their ads get clicked.
Apart from those advertisers who are buying CPM for branding..
CPMs, which can also be served as personalised ads and be on your site(s) if Gs algos consider there are no alternatives ads available, or that the other advertisers have exhausted their budget at that time, or no other advertisers have targeted your GEO IP etc etc..
I see many obvious CPMs on many sites..