Business Newsletters not big spam source

Arial Software performed an audit of the email subscription practices of over 1000 companies. http://www.arialsoftware.com/whitepapers/SpamAudit2004.pdf
What they found in their study is that signing up for a newsletter from a reputable business doesn’t get you onto any spammer lists. However, even big name companies have problems in unsubscribe requests and don’t follow what Arial feels is a best practice of double opt-in. (They dont describe double opt-in that I saw, but I assume that is where you subscribe via webform and are sent a url via email that you must click on. Then they send you another confirmation that you are really in.)