I think I might cancel. I'm not watching ads and I'm not going to pay the extra $3/mo to opt out. I don't know if I'd end up paying more than the subscription cost in shipping though....
Depends on whether or not they signed up for monthly or annual, and many get it in November so things they order show up in time before the xmas postal hell.
It seems like it would work because people wouldn't think they got their value out of their prime membership yet and are reluctant to cancel after such a short time.