The automatic renewal is pretty well spelled out when you sign up. Also, they send multiple emails a good ways out prior to charging the renewal. Or at least this has been my experience.
I'll admit that the "auto renew" verbiage may have been in the original sign up, and I just missed it or forgot about it... However, I was 100% unaware of the auto renewal charge until I received the notification from the non-Amazon credit card company that the charge had been posted against my account. If there were any emails prior to that posting, they went into the spam filter / junk email / or bit bucket...
