Vista - wait 7 minutes after booting!
I was reading a blog by Michael Woodring, called Some Assembly Required, at PluralSight, which led me to this Microsoft site on Windows operating systems as it relates to hardware. This site has a wealth of information about system internals, virtualization, and performance.
Michael probably doesn't remember me, but he vetted me as an instructor when I came aboard at Learning Tree. I was an instructor on the XML and SQL Server 2000 introduction courses.
Anyway, I have often noted that I need to boot my Vista PC and walk away from it, typically after login, to let it "settle" because it is just very slow during this phase. In the "Measuring Performance on Windows Vista" document located on this site, I came across this gem of information:
As a machine boots, large amounts of code and data are read from the disk. Systems with more than 1 GB of RAM set aside large amounts of memory for a cache of prefetched data. The system releases this cache after boot, its pages become available, and SuperFetch fills these pages with new contents. Because some of the post-boot activities throttle themselves or use low-priority mechanisms, their impact on interactive users is controlled, but they can be a source of variation in benchmarking measurements.
Benchmarking Tip: When you run workloads, delay the workload start until these post-boot activities are finished. Wait 7 minutes after boot before running benchmark workloads to reduce the variability caused by post-boot activities.