Popads.net uses an auction system where you can set minimum CPM.
Google AdSense Program Policies
I italisized the part where I think applies to pop-under Ads since these Ads are launched by a software application that the website visitor did not want to launch IMO.Traffic Sources
Google ads may not be placed on pages receiving traffic from certain sources. For example, publishers may not participate in paid-to-click programs, send unwanted emails or display ads as the result of the action of any software application.
How many popunders per 24hrs do you use?
I won't ever use popups/popunders/cpa or any other such crap on my proxies because they drive away the traffic. I want returning visitors.
I am only using adbrite for proxified pages so far and the stats are 60k impressions and 2.03 $ in my account.
I would love to sign up for another cpm netowrk though who pay better than adbrite.