Script to Find the Master Page Used

$site = Get-SPSite "http://site.domain.com"

$webs = $site.AllWebs

$webs | % {

    $obj = new-object System.Object

    $obj | Add-Member -type NoteProperty -name WebUrl -value $_.Url

    $obj | Add-Member -type NoteProperty -name Master -value $_.MasterUrl

    $obj | Add-Member -type NoteProperty -name CustomMaster -value $_.CustomMasterUrl

    $obj

} | Export-CSV -NoTypeInformation -Path "C:\folder\MasterPages.csv"