In e-commerce I've noticed that customers that request to be removed from the mailinglist and/or to have their info/account be deleted often forget about ever using the site. Then a few months later they order something and sign up for the newsletter again. When they receive their "first" newsletter they recognize the style and remember that they requested it to be cancelled, which leads to many angry emails and spam reports.

An order form with no pre-selected "join newsletter" option doesn't seem to mitigate this problem. The obvious soloution is to save the customer's email in the mailinglist as unsubscribed, but afaik that's not legal if they request an account deletion.