I just used Google Checkout for the first time and I discovered what has the potential to be a killer feature. It gives you the option of keeping your e-mail address private from the vendor your making the purchase with. From Google Checkout’s help:
Does Google share my email address with sellers?
If you’d like, Google will keep your email address confidential.
Each time you purchase something with Google Checkout, you can decide whether you’d like to keep your email address confidential. During checkout, you can select to keep your email address private. If you select to keep your email address private, Google will forward all emails from the seller to the address listed in your account, without actually sharing your real email address with the seller.
What I’d like to know is if there is some means of stopping the mail forwarding, especially if the event that the vendor decides to start spamming you.