The Tech Report has analyzed the performance of the first service pack for Windows Vista:
A quick glance through the service pack's quite considerable list of fixes, changes, and new features suggests that SP1 is indeed meant to improve Vista substantially—and not just by rolling all previously released updates into a single, neat package. High on the list are a handful of storage-related performance enhancements that cover copying files, extracting archives, or doing many kinds of file operations at once. According to Microsoft, SP1 is 25% faster when copying files within a single disk, and the "calculating time remaining" phase of file operations has been reduced to around two seconds.
Along with these welcome speed boosts, the new service pack brings a very long list of reliability, security, and power-saving improvements. That list is a little too long to sum up here, but users can look forward to everything from more consistent hard drive spin-downs, which should improve battery life on notebooks, to better driver stability in default drivers, and new application programming interfaces to help developers write more secure apps and better anti-malware tools.
Check it out over here. The reporter says SP1 isn't a magical fix but delivers plenty of improvements.