Vista Nugget: Reliability and Performance Monitor
Vista's Reliability and Performance Monitor provides you with insight into how well your system is performing. In previous versions of Windows client (and server), your system collected a variety of information about events related to system reliability and performance, but you had limited ability to visualize that information.
From the Reliability dashboard, I can view the System Stability Chart, which plots a metric of how Vista has been performing over time. This is correlated with relevant system events - such as installs of new applications - that may have impacted reliability. This provides a very useful view of Vista's stability over time that I can use to diagnose and resolve reliability issues.
More information on Reliability and Performance in Vista is here.