Does Adsense still pay $100 for each publisher you refer who earns $100? I recently got paid $5 for referring a publisher which makes me wonder whether they still offer that.
Here is a link to the program policies https://www.google.com/adsense/support/bin/answer.py?answer=25889&topic=11985 . I thought this was going to change to only US based referrals but I am not sure. I will keep checking and post again if I find that info.