This is too good, according to an infomercial at microsoft.com:
They rarely reboot Windows Server 2003 with IIS 6.0 — perhaps a tenth as often as Windows 2000 Server with IIS 5.0, they estimate. "We're seeing crazy uptime numbers now, like three months, six months. I fully expect we'll see a year of uptime when Windows Server 2003 is finished," Stucky says.
"Crazy uptimes" indeed. Crazy because it can't be a well patched and maintained box that is up for so long, regardless of operating system. Besides "availability" is a far more relevant thing to measure, but don't expect Microsofts average customer to figure that one out for another 5 years.
Jeff Stucky is the senior systems engineer on the microsoft.com operations team. He must have some clue, though it isn't evident from the above.