MY guess is that the tasted domains are being used on the ADWORDS side more than Adsense. As Ive posted before (and in some cases been censored) a lot of these tasters are using throw-away domains to take advantage of a bug in the Adwords algorithm. I won't go into it in detail to avoid further censorship (apparently because it works so well and now the cat is out of the bag with G), but suffice it to say it exploits the 'benefit of the doubt' given by G to new domains (generally MFA arbitrageurs to other PPCs) for the first few 100 impressions on each publisher for establishing a 'track record', after which the domain is no longer profitable to the advertiser.
If this is the case, and G is finally going to do something about this, I'm guessing OUR CPM as a publisher will skyrocket any day now. Something tells me they'll need to extend it to more than 5 days though, since $3 mil can still buy a lot of cheap .net and .bz domains.