On Yahoo's signup page I noticed that at least 20 million page views are required to become a publisher. Looks like adsense will be left with the lower performing sites, unless they allow using both adsense and Yahoo on the same pages.
Such as a banner for one and blocks for the other. I am looking to dump one of my lower paying adservers---not adsense though, lol
"Google won't even allow its ads on the same site with other contextual ads if these ads can minic the Adsense ads"
I can understand them wanting to protect themselves, but I think the effect they're having is that they're just pissing people off. They want exclusivity...but the targeting goess "off" quite regularly and epc bounces around like a pinpong ball. Also, smart pricing is pretty much a joke.