Great article called “Permission To Spam?” on ClickZ. Increasingly the challenge with e-mail marketing is going to be getting past the perception that your message is spam — even if you did clearly get permission.
In the long-run, smart marketers have to begin to temper expectations and realize that they have to make their lists cleaner and their messages more valuable to subscribers if they plan to succeed. For example, I know recommend double opt-in as standard for all lists. Even though it will decrease list size, it eliminates any chance of people not knowing what they signed up for. And you eliminate anyone with over aggressive filters because they never respond to the confirmation list, which means you’re less likely to be sending messages into spam filters.