It's old news that you can try Amazon Prime free for a month, which gives you free 2-day shipping on many Amazon products. (It's pretty cool, I tried it last year -- just be sure to set your account options to cancel once the trial period expires, if you don't want to be saddled with the $79 subscription fee.)
What's new is that others can now earn referral fees ($12, to be precise) if you sign up for your free trial by following their links.
So, if you want Amazon to give me free cash, and you free fast shipping, just sign up here! (Alternatively you could substitute another blogger's amazon tag in the url to help them instead. I think the folks at Crooked Timber give all their referral fees to charity, for example. Either way, you should certainly sign up with someone.)