I rebooted a Linux (Fedora Core 3) server a few weeks back, that was sitting idle on a rack and I had forgotten about. It had an uptime of 576 days when it was rebooted, but it hadnt been used for anything for well over a year (it got dropped when I went migrated to a more powerful server, and just forgotten about).
I currently have a streaming media Pentium III (Fedora Core 4), which is in production, streaming upto 70Mbps worth of audio/video at peak via Steamcast, Shoutcast, NSV and Icecast which is fast approaching one year uptime.
For a production server, thats pretty impressive. I think the longest I had a production server was 463 days, but it wasnt serving many customers in that time (it only got rebooted cos the DC had a power failiure lmao).
[root@sbp root]# uptime
05:32:58 up 316 days, 5:32, 1 user, load average: 0.00, 0.00, 0.00