Just wanted to mention something about the automated cancellation offers:
When you call to cancel, they ask for a way to identify you. You have the option of putting in your member number (you receive this in an email), your credit card number, or your phone number.
It seems that by putting in your member number, you are able to cancel without talking to a representative. If you opt to put in your phone number, you will almost certainly be transferred to a representative, who will confirm your other personal information. I do not know anybody that used their credit card number to cancel, so I don't know if you would have to speak to a rep that way.
So, if you don't want to speak with a rep, I recommend putting in your member number when cancelling (if you have it).