With the exception of reboots required by the installation of new software, my office computer has been up and running 24/7 for 10 months now.
FYI its an ASUS A7V266-E with an Athlon XP 2400 T-Bred CPU, Cooler Master HHC-001 hsf w/ heat pipes, 1 Gig PC2700 Samsung RAM running at 15 x 142 for the OC. Full load temp, per SiSoft Sandra is 59 Degrees Centigrade. However, since the temp is measured from a diode on the socket and not the actual CPU's monitor I'm led to believe the temp is regisetering high by about 5-10 degrees Centigrade. Oh yeah, it has 3 Hard drives, 2 striped 14 Gig ones and a Single 20 Gig one and is hooked to a Windows 2000 Server based network w/ SP3 installed and a Linksys Firewall/router. There are 6 other computers in the office that also run on the servers and average uptime for them has been around 3-4 months. My bookkeepers computer seems to have the most crashes (figures, its a store bought Gateway Celery instead of one I built myself).