Non optimal, quick hack when sort -unique and select -unique didn't do what I want.

psdedupe.ps1

function Dedupe {
    param (
    [Parameter(Mandatory=$true,
                   ValueFromPipeline=$true,
                   ValueFromPipelinebyPropertyName=$false,
                   Position=0)]
        $obj,
        [Parameter(Mandatory=$true,
                   ValueFromPipeline=$false,
                   ValueFromPipelinebyPropertyName=$false,
                   Position=1)]
        $property
        )
    begin {
        $uniq = @{}
    }
    process {
        $val = $obj.$property

        if ($uniq.ContainsKey($val)) {
            # skip
        }
        else {
            $uniq.Add($val, "")
            $obj
        }
    }
}