I always use jquery to animate the DOM in my design. but the problem is when user wants to see if website is working perfectly or not, for example when I have a scroller or accordion or some tools with a nice animation on the page.

So this problem is not special for me, but some time I face it.
OK, go to this address and http://flowplayer.org/tools/index.html and press Right then Left arrow key on your keyboard and then repeat it too many times quickly* and leave it to do all the animation in queue, you can see the problem, the animation is repeated on and on

So where is the problem?
take a look to this sample code of jQuery Tools main page:

// initialize scrollable and return the programming API
var api = $("#scroll").scrollable({
	items: '#tools'

// use the navigator plugin
}).navigator().data("scrollable");


// this callback does the special handling of our "intro page"
api.onBeforeSeek(function(e, i) {

	// when on the first item: hide the intro
	if (i) {
		$("#intro").fadeOut("slow");

		// dirty hack for IE7-. cannot explain
		if ($.browser.msie && $.browser.version < 8) {
			$("#intro").hide();
		}

	// otherwise show the intro
	} else {
		$("#intro").fadeIn(1000);
	}

	// toggle activity for the intro thumbnail
	$("#t0").toggleClass("active", i == 0);
});

// a dedicated click event for the intro thumbnail
$("#t0").click(function() {

	// seek to the beginning (the hidden first item)
	$("#scroll").scrollable().begin();

});

$.fn.stop() // Stop the current animation.
$.fn.clearQueue() // Clear the all job(s) in queue list

$("#intro").stop().clearQueue().fadeTo("slow", 0, function () { $(this).hide(); });
.
.
.
$("#intro").stop().clearQueue().fadeTo(1000, 1).show()

I don't have a good feeling about this, we must write it all the time and it is not good mostly when we are working on animating page, maybe is better to make a new fn function to do it:

(function ($) {
    $.fn.extend({
        c: function () {
            return this.each(function () { $(this).stop().clearQueue() });
        }
    })
})(jQuery);

Now it is more better, now we can use .c() instead of .stop().clearQueue() . for example see the code below:

$("#intro").c().fadeTo("slow", 0, function () { $(this).hide(); });
.
.
.
$("#intro").c().fadeTo(1000, 1).show()

Test it again, press Right and then Left key 1000 times, it never happens again and it will be stopped and roll backed to previews page in middle of animating.
I hope you enjoy reading this.