$query = new Zend_Gdata_Spreadsheets_ListQuery();
$query->setSpreadsheetKey($spreadsheetKey);
$query->setWorksheetId($worksheetId);
$listFeed = $spreadsheet->getListFeed($query);

//$rowData = $listFeed->entries;

foreach ($listFeed as $listEntry) {
    $rowData = $listEntry->getCustom();
    $newRow = array();
        //Populate the row data
    foreach($rowData as $field) {
        $newRow[$field->getColumnName()] = $field->getText();
    }
    //Add an array key for the new column
    $newRow['aug2011'] = 'Some data here';
        $spreadsheet->updateRow($listEntry, $newRow)
}

exit();