I definitely think they are doing network throttles. So that no one person/company owns too much of their referral traffic.
With new sites, I'm doing the same thing here. No footprints.
Any ideas, how you are going to work the ads? I'm obviously not using Adsense, but if I use the same ad company (over 2 sites); can't they just follow the publisher ID number to tell them the same thing?
I'm considering just joining every ad network known to man and every new site gets a different vendor.