Реагирование на время суток
<html>
<head>
<script language="JavaScript">
function getHourOfDay()
{       var now = new Date();
        return(now.getHours());
}

function getTime()
{
        var now = new Date();
        var minutes = now.getMinutes();
        var divider = ":";

        if (minutes<10)
                divider = ":0";

                // Hack to get it to display the time
                // correctly in version 3.0, (adjust 
				for offset)
        if (navigator.appVersion.lastIndexOf('3.')
		 != -1 &&
                navigator.appName.lastIndexOf
				('Netscape') != -1)
                        return( now.getHours()-1
						 + divider + minutes );

                // Other versions may work with this ?
        return( now.getHours() + divider + minutes );
}

function sayHello ()
{

        document.write( "Сейчас <B>" +
                                getTime() +
                                "</B>, 
								поэтому мы желаем Вам" );

        if(getHourOfDay()<5 || getHourOfDay()>19)
                document.write(' спокойной ночи!');
        else
        {
                if ( getHourOfDay() < 11)
                {
                        document.write(' доброго 
						утра!');
                }
                else
                {
                        document.write(' хорошей 
						работы!');
                }
        }
}
</script>

</head>
<body>
<script language="JavaScript">
<!--
sayHello()
// -->
</script>
</body>
</html>