Over 22 days may well be the current record. My lovely 12″ 867 MHz Powerbook has now served me faithfully (even though the factory hard drive did not) for three and one-half years. I cannot justify buying a new Mac because save for occasional speed problems, this baby stays up and running without reboot no matter how much punishment I dish out: working with 20 megabyte data files, compiling hundreds of megabytes of software, closing opening and closing and opening applications over and over, having Microsoft programs (and Apple programs on occasion) crash, installing new software and moving daily between a wired and a wireless networking environment. Never a hitch, never a hickup.
On this day in February 1997, the streak had to end because new operating system updates required a reboot. 🙁