I had to restart today at work. I’m using Windows 2000 and I haven’t restarted once in the last 66 days, 7 hours, and 26 minutes—a personal best!
My second best uptime record was over 47 days on my PowerBook G4 running Mac OS X 10.3. A power user running Mac OS X will rarely have an uptime over about 45 days because Apple releases OS and security updates that require a restart and you mustn’t pass those up. Microsoft rarely updates Windows 2000 and most security updates are related to Internet Explorer, so you can get much higher uptimes.