Google has silently added an option to display referral links (with images) in your blog or web sites.

If anyone referred by you earns 100$ or more then Google credits your account with 100$.

When a user you’ve referred to Firefox plus Google Toolbar runs Firefox for the first time, you’ll receive up to $1 in your account, depending on the user’s location.

You can track your earnings from referrals by visiting your Overview page. Monthly totals of referral credits will appear on your Payment History page. Your earnings from referrals will be included with your earnings from AdSense for content and AdSense for search.
Link

You can choose your referral image here.

Sounds like a good deal to me.

Google also made revision to its terms of service. I haven't gone through the details but it looks innocuous on surface.