GetCheckedRows() method returns object of HTML RowElement collection. In order to access the cell value or text of the checked rows, I suggest you to convert the HTML RowElement collection (returned by GetCheckedRows() method) into WebGridRow object first. After get the WebGridRow object, then you can access its cell value and/or text or any properties related to the respective cell.

Below is the snippet code that shows how to do the conversion plus how to obtain the cell properties.

<script type="text/javascript">
    <!--
    function GetCurrentCheckedRows()
    {
        // retrieves WebGrid's object
        var grid = ISGetObject("WebGrid1");

        // access WebGrid's RootTable
        var rootTable = grid.RootTable;

        // get the current CheckedRows (return HTMLElement)
        var checkedRowsElement = grid.RootTable.GetCheckedRows();
        for (var i = 0 ; i < checkedRowsElement.length ; i++)
        {
            // convert HTMLElement to WebGridRow object
            var row = rootTable.ToRowObject(checkedRowsElement[i]);
            alert(row.GetCells().GetNamedItem("CompanyName").Text);
            alert(row.GetCells().GetNamedItem("CompanyName").Value);
        }

        return true;
    }
    -->
</script>

Hope this helps.