Microsoft released a document about high availability at Microsoft.com website and how they structure their environment and the most import how they monitor it.
If High Availability is one of your favorite topics this article is a must read.
Microsoft.com is a large and heavily visited site, yet it maintains high availability ratings because of a carefully planned infrastructure, team collaboration, and use of technology for maintenance, monitoring, and change management.
Download the article at http://www.microsoft.com/downloads/en/details.aspx?FamilyID=84c59af0-da50-49bf-84e3-dd3f5bd6c0cd
Cheers,
Anderson Patricio
http://blogs.msexchange.org/patricio
Twitter: @apatricio