Microsoft has released a white paper which compares feature and capabilities of Windows XP SP3 with Windows Vista SP1. Using this comparison, customers can adjust their expectations for the security, management, deployment, mobility, and productivity of either operating system. For each feature or capability section compares key Windows Vista advancements against Windows XP.
Its a white paper which clearly shows how Windows Vista is superior to Windows XP with those compared features. So this document will be a good help in deciding for those who were waiting to switch to Vista from XP. This document makes a good read where features are compared in a tabular format with key differences shown.
You can download the document here. Its available in pdf format (737 KB ) or in xps format (580 KB) file.