System Uptime

C:\>systeminfo | find "System Up Time"

Will tell you how long since a computer's been rebooted. I use this when someone has a problem and SWEARS that they rebooted their PC four times this morning.

"Umm... well it says here you haven't rebooted since March. You know sleep and hibernate don't count, right?"

Notes:
Hibernate is an interesting beast, because it allows you to physically reboot the hardware without rebooting the software. I once hibernated a PC and replaced the hard drive. Several months later, I reinstalled the original drive to check something, and systeminfo reported the uptime as months.

Also, as always, FIND is case sensitive.