There are two significant performance and reliability patches available for Vista that have not yet been released through Windows Update. You can go and grab them from Microsoft’s site, though.
I installed them today, and I think that I’m already seeing some improvements, specifically coming back from hibernation on my laptop. Some Office apps also seem a bit peppier, but it’s all subjective, isn’t it?
From what I’ve read on the Web, Microsoft is intending to release the contents of these two patches as part of SP1, which is expected sometime soon, but why wait?