Paul mentioned this a couple of days ago. He and two other Exchange MVPs wrote a nifty little pocket guide with "top 10" list of availability principles and tips for Exchange.
"It's a very bad day when Microsoft Exchange goes down.
Unfortunately, achieving high availability with Exchange can be a daunting task: a wide variety of software, hardware, directory, storage, network, and datacenter problems are always lurking. Each one has the potential to bring email down.
There are many causes of downtime: an idiot with a backhoe cutting the fiber line, an executive emailing his 7 GB ripped video of a Grateful Dead DVD, termites in the data center, a night visitor accidentally shutting down power - not to mention the mundane failures caused by human error, technical problems, and natural disasters.
This pocket guide provides 10 essential rules that will help you ensure that email is always available, no matter what. It was written by three Microsoft Exchange MVP's to help Exchange Administrators avoid many of the pitfalls that can lead to painful downtime."
The Microsoft MVP Guide to Exchange Availability: 10 Essential Rules that Will Save Your Job is available as a download at the Windows IT Pro site (registration is required).