First, referral ads are credited on a cost per action (CPA) basis. This means that there is a specific action such as an install for Google Pack that your visitors must complete before you generate earnings. The advertiser places a certain value on that action being completed, and is willing to pay you a percentage of that value. If you highlight the referral ad and encourage more people to complete the action, the value that the advertiser places on that action does not diminish.

For example, Google is willing to pay up to $2 for each new user who downloads and installs Google Pack. If you encourage people to download and install Pack on your site and the conversion rate goes up, we're happy to pay the additional cost, because it directly translates to more Pack users for us.

However, this isn't the case for most AdSense for content and AdSense for search ads, which are served on a cost per click (CPC) or cost per thousand impression (CPM) basis. It's generally harder for an advertiser to decide on a CPC/CPM value than it is to decide on a CPA value because multiple factors go into deciding the value of a click or impression. Encouraging clicks on these ads not only drives lower quality traffic to an advertiser’s site but provides poor data for an advertiser to make an appropriate bid on the click. This results in a poor experience for visitors and advertisers, which isn’t good for you as a publisher.

Additionally, you can endorse referral ads because you know the exact ad you are displaying on your site. You are offering your visitors genuine advice based on the products and services you think they'll like. However, with CPC ads you don't know which ads will show up -- it would be disingenuous for you to recommend the products or services in your ads in this case, which could result in visitors being misled.

Of course, publishers may never encourage people to click on any ad, including referrals, for deceptive purposes. For example, you can't ask visitors to click on a referral ad to make you money. Any endorsement or attention drawn to a referral ad must be done in a way that supports the intended use of the product or service associated with it.

In short, our policies on endorsing ads are based on our concern for the visitor, the advertiser, and the publisher. We strive to make AdSense work best for all our partners.

Posted by Dan Friedman - AdSense Product Marketing

AdSense 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 $5When 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).

AdWords Referrals:

When an advertiser you refer spends $5 within 90 days of sign-up (in addition to the $5 sign-up fee) you will be credited with $5.

When that same advertiser spends $100 within 90 days of sign-up, you will be credited with an additional $40.

If, in any 180 day period, you refer 20 advertisers who each spend more than $100 within 90 days of their respective sign-ups, you will be awarded a $600 bonus (bonus payments are limited to 1 per year).

These rules will also apply to users that you have already referred but who have not yet reached one of the new earning/spend thresholds. For example, if you referred an AdSense publisher who has currently earned $2.00, you will be paid $5.00 if that publisher reaches the $5.00 mark. But, if you have referred an AdSense publisher who has already earned $10.00, you will not be paid $5.00 retroactively for that referral reaching the $5.00 mark. However, should that publisher eventually reach the $100.00 earnings mark within 180 days, you will be paid $250.00.

Finally, please keep in mind that publishers may not click on their own referral ads and will not be paid for referring themselves for any product. For more information about referrals, please visit our Help Center.

Posted by Dan Friedman - AdSense Product Marketing