Find duplicate MAC addresses

In the physical world duplicate MAC addresses rarely happened. In the virtual world this can happen quite easily. How to find those?

A little PowerCLI script that looks through all VMs in a vSphere cluster / vSphere host and sorts entries by MAC addresses:

Connect-VIServer [server name]
Get-VM | Get-NetworkAdapter | select MacAddress,Parent,NetworkName | sort MacAddress


Update: see also 2nd entry: http://adminthoughtcollection.blogspot.com/2011/08/find-duplicate-mac-addresses-2.html