As far as I can remember, YPN only allows publishers from U.S. However, there are some non-US sites have some YPN advertisements running. Here I cut-and-paste a statement from the registration page:
Participants of the program must have a valid U.S. Social Security or Tax ID number, and web site content that is predominantly in English and targeted at a U.S. user base.
Having nothing to do, I give it a try and see what kind of response I'll receive from Yahoo!, although it is quite clear that it's going to be a negative response. Just for your information, I entered 'No' for the question 'Do you Have a Valid U.S. Social Security or Tax ID Number?'.
Anyhow, it's really interesting to know whether they will generate better income than Google AdSense.
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