I used to have this Debian box (which was a PowerMac G4) in my hallway. It had a 1000+ day uptime, back when this kind of uptime was still cool, or at least I thought it was. At some point it was two major versions behind, and I decided to dist-upgrade it. To my amazement, the upgrade went flawlessly, and the system booted without problems afterward. Debian is just great like that.