Rufal - 2:57 pm on Mar 23, 2011 (gmt 0)
I once tested US versus "rest of the world". Did it by creating two identical ads, and showing one for US traffic (Using geolocation based on IP) and the other "for the rest".
It came to no surprise that the US one had a much higher eCPM then the others (being about 35% of traffic).
But it didn't change anything in overall income. It's just that some countries do not give you much value, hence lowering the eCPM. But I still want the revenue from those countries, even though its a much lower eCPM, it's still something I wouldn't otherwise have.