Sample script that search Active Directory for all inetOrgPerson accounts modified on October 1, 2007 or later. The whenChanged attribute is replicated to the Global Catalog. This means you can connect to a Global Catalog server and search across the forest for all inetOrgPerson accounts last modified on a specified date.

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$strFilter = "(&(objectCategory=inetOrgPerson)(whenChanged>=20071001000000.0Z))"

$objDomain = New-Object System.DirectoryServices.DirectoryEntry

$objSearcher = New-Object System.DirectoryServices.DirectorySearcher
$objSearcher.SearchRoot = $objDomain
$objSearcher.PageSize = 1000
$objSearcher.Filter = $strFilter

$colProplist = "name"
foreach ($i in $colPropList){$objSearcher.PropertiesToLoad.Add($i)}

$colResults = $objSearcher.FindAll()

foreach ($objResult in $colResults)
    {$objItem = $objResult.Properties; $objItem.name}