Microsoft recommends upgrading from IE6 to IE8 for better security

I agree with this recommendation as IE8 offers better security than any past release.  As IE6 is on very limited support, some security holes may never be patched.  IE8 offers improved protection from spyware, phishing, malformed webpages, and malware attacks.  It is more actively maintained by Microsoft and it was better designed from a security perspective. 

One  issue in upgrading would be a vital website application that does not support IE8. Most webmasters have addressed these issues as IE8 has been out for several months.  Even if issues occur, IE8 can safely uninstalled to revert back to IE 6 if needed.

Try it, you'll like it much better than IE6 -- at least I do

Microsoft's IE 8 Effective at Blocking Phishing, Malware, Report Says
http://www.eweek.com/c/a/Windows/Microsofts-IE-8-Effective-at-Blocking-Phishing-Malware-Report-Says-225292/
http://gcn.com/articles/2009/08/14/ie8-security-report.aspx

QUOTE: Microsoft's Internet Explorer 8 Web browser is effective at blocking both phishing sites and socially engineered malware, according to two new NSS Labs reports. In turn, this has led Microsoft to push for its users to upgrade to the new browser from IE 6 and IE 7, which a significant portion of the community continues to use.