(1) an e-mail recipient cannot be required to pay a fee, provide information other than his or her e-mail address and opt-out preferences, or take any steps other than sending a reply e-mail message or visiting a single Internet Web page to opt out of receiving future e-mail from a sender;These changes appear to tighten up what is required of marketers; they have to say who they are and they can't weasel out by claiming a corporation is not a person.
(2) the definition of “sender” was modified to make it easier to determine which of multiple parties advertising in a single e-mail message is responsible for complying with the Act’s opt-out requirements;
(3) a “sender” of commercial e-mail can include an accurately-registered post office box or private mailbox established under United States Postal Service regulations to satisfy the Act’s requirement that a commercial e-mail display a “valid physical postal address”; and
(4) a definition of the term “person” was added to clarify that CAN-SPAM’s obligations are not limited to natural persons.
— FTC Approves New Rule Provision Under The CAN-SPAM Act, Press Release, FTC, May 12, 2008
However, it's not clear to me why it's opt-out that's required; why not opt-in? I never trust a spammer to process an opt-out; I assume they're just collecting more addresses. Plus the spammer still has ten days to process opt-out requests.