Here's Laura Chen, answering questions about the policies related to AdSense referrals in this pre-recorded video from the Googleplex. Laura addresses these burning questions:

1. Why am I receiving less than the full amount for each conversion in my reports? Is something wrong?
2. After I've referred a person to AdSense, can I see how much they've earned so far?
3. Can I ask users to click my referral buttons?

As Laura notes, you can find more information about referrals in the AdSense Help Center, and don't forget, in the recent program policy update, you can now display more referral units on your pages.

AdSense Blog

Goolge, Online+Video, Laura Chen, Googleplex, Referrals