According to Stefan, Google changed their policy and now pay you upfront. Here is the email he received from Google:
Thank you for the email. I’m happy to say that we’ve now changed the payment model for referrals so you’ll earn more from now on. You’ll, as it has happened, get $5 when a user you’ve signed up earns $5. When the user has earned $100 and complies with the general terms of service for referrals you’ll get additionally $250 on top of the $5 - total $255. This is brand new and we’re right now updating our help center with this information.
So you earn money right away and then if the AdSense or AdWords sign up actually makes Google enough money, you earn more money. This program is much more enticing then the previous affiliate rules.
Update: It is official, a Google Adsense blog post named new pricing structure for referrals updates on this.