$('#topnav').bind({

                            mouseenter: function() {
                                $("#topnav").animate({opacity: 1.0, width: '98%', height: '38px'});
                            },
                            mouseleave: function() {
                                   $("#topnav").delay(2000).animate({opacity: 0.9, width: '310px', height: '33px'});
                            }

                            });

var tout;
$('#topnav').bind({
  mouseenter: function() {
    clearTimeout(tout);
    $("#topnav").animate({opacity: 1.0, width: '98%', height: '38px'});
  },
  mouseleave: function() {
    tout = setTimeout(function() {
      $("#topnav").animate({opacity: 0.9, width: '310px', height: '33px'});
    }, 2000);
  }
});

var timeout = null
var onMouseEnter = function(){
  clearTimeout(timeout)
  $("#topnav").animate({opacity: 1.0, width: '98%', height: '38px'})
}

var onMouseLeave = function(){
  timeout = setTimeout(function(){
    $("#topnav").animate({opacity: 0.9, width: '310px', height: '33px'});
  },1000)
}

$('#topnav').bind({ mouseenter: onMouseEnter, mouseleave: onMouseLeave })​