Screaming Penguin - Source Does Matter

Yeah! Microsoft has acheived 99.999% uptime with Windows 2000. And how do we know this, because Starbuck is using them (thats about as much detail as the article gives us).
Here's a snippet from their press release:
"The development team analyzed nearly 1,200 servers running Windows NT Server 4.0. They learned that 65 percent of system reboots were due to planned outages for routine administrative tasks such as adding hardware and applications. By ignoring both planned and unplanned outages in Windows 2000 testing, we were able to acheive a perfect 5 nines rating, a remarkable improvement."
  Microsoft Article