I ran red hat linux for a while and didn't shut down for two months. I run Windows XP and the longest I went without shutting down was three months. Then SP2 came out and I had to reboot. Windows 98 was recommended that you reboot at least once a day. Windows ME recommends you reboot at least once a week. Windows 2000 recommends every two to three weeks. Windows XP has no recommendation on reboot amounts or times.