I just launched 2 traffic campaigns with them a week and a half ago, and the results have been disappointing to put it mildly... I have raised my bid 10x and traffic is still trickling in at a snails' pace - no matter what.
I have: Expanded Geos to include ALL tier 1 & Tier 2 countries
Increased my bid on Pop's and Banners 10x, well above the rates that it claimed the "average" advertiser was bidding in their traffic estimator tool..
Expanded to accept from all carriers
Added new banners
Double checked the click ratio on existing banners
My findings: After a week and a half, I've only managed to spend $0.60 some odd cents of my Popunder budget, and my banners have made a whopping 4 impressions, but were clicked 2 out of those 4 times....
Also, the pop traffic I DID receive had a 100% Bounce rate with an average traffic duration of 3 seconds....
Not a happy camper!