<script type="text/javascript">
$(document).ready(function(){
$('#topnav li')
.mouseover(function(){
    $(this).stop().animate(
        {'background-position-y': '28px'},
        {opacity: 1},
        {duration:100})
    })
.mouseout(function(){
    $(this).stop().animate(
        {'background-position-y': '38px'},
        {opacity: 0.3},
        {duration:100})
    })
});
</script>

<script type="text/javascript">
$(document).ready(function(){
$('#topnav li')
.mouseover(function(){
    $(this).stop(true).animate(
        {'background-position-y': '28px', opacity: 1},
        {duration:100})
    });
.mouseout(function(){
    $(this).stop(true).animate(
        {'background-position-y': '38px', opacity: 0.3},
        {duration:100})
    });
});
</script>

$(this).stop().animate({
    'background-position-y': '28px',
    'opacity': 1
}, 100)