These are links to KB articles indicating some unsupported practices in SharePoint and at random. 

 Restoration of the configuration database is not supported in SharePoint Server 2007 and in Windows SharePoint Services 3.0
http://support.microsoft.com/?id=948725

The Windows Server 2003 /3GB switch is not supported in Windows SharePoint Services 2.0 or in later versions or in SharePoint Portal Server 2003 SP2 or in later versions
http://support.microsoft.com/kb/933560

Supported and unsupported scenarios for working with custom site definitions and custom area definitions in Windows SharePoint Services, in SharePoint Portal Server 2003, and in Office SharePoint Server 2007
http://support.microsoft.com/kb/898631