I'm registered to Google AdSense and I've the ads block and some AdSense referrals buttons on my Italian blog.

Yesterday, looking at my earnings I noticed that I was giving 5$ for the AdSense referral product. I knew that for that product the rule was:

When a publisher who signed up for Google AdSense through your referral earns their first $100 within 180 days of sign-up, you will be credited with $100.

So why did I get $5? I thought that it was very difficult for someone that signs up for the first time to reach $100 in 180 days, so they should have changed something, and looking back in the AdSense blog archives I found the answer: in February they changed the pricing structure for referrals:

When a publisher who signed up for Google AdSense through your referral earns their first $5 within 180 days of sign-up, you will be credited with $5.

When that same publisher earns $100 within 180 days of sign-up and is eligible for payment, you will be credited with an additional $250.

If, in any 180-day period, you refer 25 publishers who each earn more than $100 within 180 days of their respective sign-ups and are all eligible for payout, you will be awarded a $2,000 bonus (bonus payouts are limited to 1 per year).

I don't think I'll ever receive $250, but probably I'll start receiving a few $5 earnings for some of the signups performed through my referral button.