Somewhat fittingly, Service Pack 1 very much mirrors Windows Vista itself in the way it delivers (or fails to deliver) on users' expectations. If you were looking for across-the-board system performance improvements or major new features, prepare to be disappointed. Our benchmarks suggest SP1 does significantly speed file manipulations, and we confirmed those results with our seat-of-the-pants tests while copying and deleting local files during everyday usage. However, like Vista, most of the service pack's improvements are under the hood and probably won't be immediately obvious to the average user.

http://techreport.com/articles.x/14463