So I'm on the phone right now with amazon.com (yes, they have a phone number) because evidently, they didn't feel like it was enough to charge me just once for my "Prime" membership.
When I was paying bills today, I noticed a random $79 charge from amazon.com on our credit card. I signed up in January and promptly hit the "don't renew" button for my one year membership.
I guess a one year membership isn't a one year membership sometimes?? Caveat emptor.