From a consumer advocacy standpoint, I consider regulations (e.g, CAN-SPAM Act) to be the absolute minimum to live by.
For instance, as long as e-mail marketers leverage permission-based marketing, provide value and authenticity in their e-mails, they will not need to have concerns over legal compliance. The laws only supplement good e-mail practices.
I support the metaphor, "Don't put the milk in the back of the fridge." Which means, don't make the value of your content so deep or place barriers to obtain the value of your content. Likewise, don't let the milk spoil by leaving the content out without some sensible path to obtain it.
Every small business will have to trial with different products and information and see how their clients react.
On a similar note, Seth Godin (another eMarketing genius), has a verbose checklist that EVERY e-mail marketer needs to run through before sending. You can check it out at:
http://sethgodin.typepad.com/seths_blog/2008/06/email-checklist.html~Joe