For those in the audience running Windows XP, the following can be copied and pasted into a .txt file, renamed with a .bat extension, and run whenever you find yourself curious about the duration since your last reboot/BSOD.
@systeminfo | @find "System Up Time:"
This code will search through the systeminfo file, and return the length of time your system has been running in "x day, x hour, x minute, x second" format.

Place the file in your Windows directory so that you can execute it from the Run menu, or simply create a shortcut to it on your desktop.

It should be noted this will only work with Windows XP Professional; the Home edition of Windows XP lacks the commandline version of the SystemInfo utility.

For those with Windows NT Server 4.0 SP4 and above, or Windows 2000, you can always download the uptime executable from Microsoft to reassure you about your system stability. Just launch your browser over to