TRos,
частая ошибка
<script>
function setOpacity() {
var op = 0;
setTimeout(function (){
if (op > 1) return;
document.getElementById('big').style.opacity=op;
op+=0.1
setTimeout (arguments.callee, 100);
}, 100);
}
</script>
<div id="big" onClick="setOpacity();" style="opacity:0.1">
blah-blah-blah...
</div>