Today I tried to signup with YPN i.e Yahoo Publisher Network Beta. But in terms and condition section, I came to know that for using YPN I must have US address, plus a US Social Security number or a US IRS tax ID number. Unlike adsense, it does not support international publishers because at the moment, YPN is still in beta testing. Also YPN is not returning ads that are as relevant as the ones that Adsense users are finding on their sites. But I am confident YPN will go international within one year. By the way, you will love to see the comparison chart of adsense and YPN.