Lately there are more and more site owners getting rather angry at Site Advisor. It is explained well on http://siteadvisorclassaction.com/ but you can just google "SiteAdvisor complaints" to see there is a common theme.
Even more concerning is that lately there are a number of claims that site owners are being told they can buy their way out of a poor rating - and it seems SiteAdvisor is unfairly rating sites bad that are rated good everywhere else - perhaps to "encourage" the site owners to purchase the expensive McAfee "certification".
If you are running SiteAdvisor be aware that the credibility of any ratings are seriously suspect - and poor ratings may be seriously out of date - and SiteAdvisor will not correct their error or rescan the site until after the site purchases an expensive "site certification". (many people would see this as nothing less than extortion).
http://bitsum.blogspot.com/
http://siteadvisorclassaction.blogspot.com/2008/06/mcafee-site-advisor-run-amuck.html
http://www.snapfiles.com/siteadvisor.html
http://muquit.com/
http://windowssecrets.com/2009/02/19/01-McAfee-reveals-SiteAdvisors-retesting-policy
http://forums.scotsnewsletter.com/lofiversion/index.php/t21610.html
http://info.mapzone.net/2006/mcaffee-siteadvisor-slams-coffeecup-software.html
http://www.404techsupport.com/2010/03/18/whats-the-harm-in-mcafee-siteadvisor/