This good news reflects active work in shutting down botnets that generate spam messages. Users should still vigilant and use best practices.
EMAIL SPAM Rates continue to decline
http://securitywatch.pcmag.com/security-software/286379-spam-continues-to-decline
http://blogs.msdn.com/b/tzink/archive/2011/08/15/spam-continues-to-drop.aspx
QUOTE: Multiple sources indicate that spam is in a continued decline as a portion of overall e-mail. One such measure, from spamcop.net, shows the decline pretty clearly. Since mid-2010 the amount of spam is down over 75%.