Expanding on mjswensen's answer, the command without the filter could take minutes, but the filtered command is almost instant.
PowerShell - List local user accounts
Fast way
Get-WmiObject -Class Win32_UserAccount -Filter "LocalAccount='True'" | select name, fullname
Slow way
Get-WmiObject -Class Win32_UserAccount |? {$_.localaccount -eq $true} | select name, fullname