WoodITWork.com

Hugo Peeters has a great function for using WMI to get Logged on Users:
http://www.peetersonline.nl/index.php/powershell/oneliner-get-logged-on-users-with-powershell/

This can be easily used in PowerCLI.  This can be very useful when you need to do some VM maintenance in a VDI environment and need to find out who is currently logged on and know which VMs are not in use and can be worked on.

$VMs = Get-Cluster "LON_PROD1" | Get-VM | Where { $_.PowerState -eq "PoweredOn" }
ForEach ($VM in $VMs) {
	Write-Host "Logged On Users for: " $VM.Guest.HostName
	Get-WmiObject Win32_LoggedOnUser -ComputerName $VM.Guest.HostName | Select Antecedent -Unique | %{"{0}\{1}" -f $_.Antecedent.ToString().Split(’"‘)[1], $_.Antecedent.ToString().Split(’"‘)[3]}
}