Jeff Jones, Security Strategy Director in Microsoft's Trustworthy Computing group, (a former security consultant to the Air Force, NSA and product manager for McAfee) has released a one year vulnerability report on Windows Vista. The .PDF file is 744k.
The results of the analysis show that Windows Vista has an improved security vulnerability profile over its predecessor. Analysis of security updates also shows that Microsoft improvements to the security update process and development process have reduced the impact of security updates to Windows administrators significantly compared to its predecessor, Windows XP.
Windows Vista One Year Vulnerability Report : Welcome To Tech-Dump
Windows Vista One Year Vulnerability Report : Welcome To Tech-Dump