On their leaderboard there was an NT4.0 machine with several years of uptime. People accused the owner of having manipulated the reporting tool, but the owner said it was just being used as a secondary DNS server internally at a company, and scheduled to be replaced as soon as the hardware fails. I don't know whether that happened before the site shut down unfortunately.
But, it turned out there was a bug in our earlier agent version that wrapped the uptime at 365 days and all their servers were well over that. They'd had warnings set at a year and critical at 18 months/2 years, some high value.
I asked if they were worried, and apologized for the bug. They said it wasn't a problem and just increase the thresholds so it was all green again and they'd get around to rebooting at some point.
I tried powering it back online afterwards. It did not power back on.