have_ballooned.ps1

# Find all of the VMs that have experienced ballooning in the last day
function ballooned? ($vm) {
  $d = Get-Stat -memory -entity $vm -start (Get-Date).AddDays(-1) |
    ?{ $_.MetricId -eq 'mem.vmmemctl.average' } |
    ?{ $_.value -ne 0 }
  return $d.count -ne 0
}

connect-viserver -server virtualcenter -credential (Get-Credential (Get-Item env:username).value)
$vms = get-view -viewtype virtualmachine
$vms | ?{ ballooned?( get-viobjectbyviview -moref $_.moref ) } | %{ $_.name }