While Windows has long included administrator-oriented performance and reliability monitoring tools, they were never of much use to end-users, unless of course your idea of excitement is to watch line graphs update in real time. With Windows Vista, that's all changed: A surprisingly interesting new tool called Reliability Monitor provides an ongoing snapshot of your PC's reliability, and this information is useful for troubleshooting regardless of what kind of user you are.
Before the advent of Reliability Monitor, Windows users had few ways in which to accurately determine how well their PCs were performing. Essentially, you would install the OS, a hardware device, or software application, or perhaps you would update the driver for an existing device. Any one of these actions could cause the PC to work better or, in the more memorable experiences, cause it to swoon wildly out of control, perhaps blue-screening down to a hard stop. In such cases, you would have to rely on your own memory to figure out what happened: Was it the RAM I just installed? Or perhaps that Adobe software update? Sometimes you'd simply never know.
Windows Vista builds on the troubleshooting tools provided in previous Windows versions to help you figure out what's going on with your PC. There are older tools like Performance Monitor, Event Viewer, and the Disk Defragmenter that have been improved somewhat in Vista. And then there are tools that are brand new to Vista. Reliability Monitor is the most useful of those new tools.
Because Microsoft considers the Reliability Monitor to be an advanced diagnostic tool--which I think is ridiculous, by the way--it is hidden away in the Reliability and Performance Monitor management console. You can access this console, which includes the updated version of the Performance Monitor in addition to the new Reliability Monitor and a cool Resource Overview view, in a variety of ways. There are a variety of ways to launch this tool, but the simplest is to type "relia" (no quotes) in Vista's Start Menu search box and clicking the link that appears for Reliability and Performance Monitor.