Techreport analysed the performance of the recently released SP1 for Windows Vista.

Quote from the report: "How does Service Pack 1 affect Windows Vista's day-to-day performance in common desktop applications and games? We've run a host of benchmarks in order to find out.
To assess SP1's impact on performance, we performed a clean installation of the "release-to-manufacturing" (i.e. original retail-boxed) edition of Windows Vista Home Premium x64 on our test system, and we ran a first round of benchmarks with no patches and only necessary drivers applied. Then, we downloaded the x64 Service Pack 1 standalone installer from Microsoft's Download Center, installed it, and ran our suite of benchmarks again."
Read the full report on TechReport.