AnandTech has a great review of Vista SP1. A few interesting Quotes:
Possibly why SP1 benchmarks lower than preSP1?:
One thing that is unfortunate for Microsoft with SP1 is that there is a good chance that system performance immediately following the patching process will be lower than it was prior to patching. As part of the installation process the SuperFetch and ReadyBoost subsystems are purged of all caches and learned behaviors, effectively reverting a patched system to that of a brand-new untrained system. Vista does not take long to retrain itself, and Microsoft notes the process can take a couple of days (we were back to perceived normal within a day), but nevertheless a lot of people are going to be thrown off by things such as longer application load times immediately following the patch.
Less UAC prompts:
Among the most significant fixes to Vista in SP1 is Microsoft’s work on further refining the User Account Control (UAC) prompts of Vista…An adjustment to the folder creation is the most prominently touted of these fixes, with the number of folder creation prompts (when creating a folder in a protected location) falling from four to one. Microsoft doesn’t list any further reductions in UAC dialogs, but as far as anecdotal evidence is concerned it certainly feels like they’ve done a bit more than that. This won’t change the public perception of UAC (or Apple jokes on the subject), but any reduction is welcome and perhaps will stem the tide of Vista users who are completely turning off this critical system feature.
Well, at least it can see it:
For anyone who has a system running a 32-bit version of Windows and 4GB of RAM, they will be well aware that in 32-bit mode not all of that RAM can be addressed, and that Windows reports the amount that can be addressed accordingly. With Vista SP1 Windows will now be reporting the amount of RAM in the system, and not the amount that can be addressed. The advantage of this is that it will reduce the number of computer owners thinking something is wrong because Windows doesn’t “see” all of their RAM; on the other hand this is clearly disadvantageous because they will no longer be informed that Windows in fact isn’t using all of their RAM, nor will there be an easy way any longer to tell how much RAM it is capable of using.
Benchmarks – For the most part their benchmarks showed either no change or a very slight advantage for SP1.
At this point it’s clear that what performance improvements Vista does offer are limited to a handful of situations where we are specifically file or network I/O bound. What this means for any given application is that it is unlikely to see a performance improvement due to SP1…
While shutdown time doesn’t see any real performance improvements, we are surprised to see an improvement in startup time by several seconds. Vista is not notably slow to start up in the first place, so we weren’t expecting much improvement if there was to be any at all. Shaving off 5 seconds for a 14% improvement in startup time (getting startup below 30 seconds altogether) is a pleasant surprise.