Try reading this blog post: http://widgetbucks.blogspot.com/2007/12/international-cpm-q.html That's the only information they give about this. If you're looking to sign up you're in luck - I'm still looking for referrals in my sig!
on a related note, why would the CPMs for international traffic be so low when we actually see quality ads displayed - its not as if its a unknown advertiser - looks like Widgetbucks is eating up 90% of the traffic . .the CPM for me is as low as 5 cents!!