When troubleshooting a MOSS environment that I didn't design/build, the first thing I look to do is confirm that appropriate domain accounts have been used for all the application pools. Rather than working the MMC UI, I just run this script...

C:\WINDOWS\system32>iiscnfg.vbs /export /f c:\iisAPPpoolConfig.xml /sp /lm/W3SVC/AppPools /children

This will produce a nice list of the application pools. E.g.

<IIsApplicationPool    Location ="/lm/W3SVC/AppPools/SharePoint Central Administration v3"

        AppPoolAutoStart="TRUE"

        AppPoolIdentityType="3"

        IdleTimeout="10"

        PeriodicRestartSchedule="02:12"

        PeriodicRestartTime="0"

        PingingEnabled="FALSE"

        RapidFailProtection="FALSE"

        WAMUserName="domain\account"

        WAMUserPass="blablabla"

    >

</IIsApplicationPool>

What I don't want to see is all the application pools using the same domain account or built in accounts (System or Network service).

Some notes on appropriate IIS Application Pool settings can be found on Joel Olsen's blog
http://blogs.msdn.com/joelo/archive/2007/10/29/sharepoint-app-pool-settings.aspx

Appropriate Active Directory Domain Account usage for SharePoint can be found here...
http://www.wssdemo.com/redir.aspx?ID=1456

The other things I like to check are:

• SharePoint Windows Services identities
• Content Database information (location, size etc)
• Site Collection Details
• Logging setup (get stuff off c: )
• Search configuration (this is the one that goes wrong the most)

More tips to come...