Monetizing your website...the overlooked inventory

In this day and age of standard ad units, mobile ad units, social media ad units, video, pop overs, unders and everything in between...I am often amazed of the amount of open inventory that is so often overlooked by website owners and publishers and has the highest potential revenue per visitor....the registration pages and forms of the site. My question is two part and will probably spark some thought and discussion... 1) Who is monetizing their registration forms on their websites (newsletter sign up forms, contact us, shopping carts, etc.) and if you are, how are you doing it? Google ads? Transparent and audience relevant co-registration? More of the same standard IAB ad units? 2) The second portion of the question for those that are monetizing their forms, what kind of CPMs are you generating from your efforts?