Best uptime I ever had was on a freebsd box. Which was about 111 days before the power went out. I have an OpenBSD box that I never reboot at the moment. However my power seems to enjoy going out. It was last rebooted upgrading from 3.6 to 3.7.
-bash-3.00$ uptime
10:03PM up 4 days, 12:52, 1 user, load averages: 0.17, 0.12, 0.09
AND THATS THE MOST STABLE MACHINE I HAVE.
Well theres my firewall...
x11@minamoto ~$ uptime
12:14:21 up 34 days, 2:46, 1 user, load average: 1.05, 1.01, 1.00