It would be nice to exchange places of triggering sortstart event and hiding element with visibility:hidden.

I.e. this:

$(this.element).triggerHandler("sortstart", [e, that.prepareCallbackObj(this)], o.start);
$(this.element).css('visibility', 'hidden');

should become this:

$(this.element).css('visibility', 'hidden');				
$(this.element).triggerHandler("sortstart", [e, that.prepareCallbackObj(this)], o.start);

doing so will give more control for interface designers to style their sortable elements behaviour.

Example of usage:

stuffContent.sortable({
    start: function (e, el) {
        $(this).css({visibility : "visible", opacity: "0.15"});
    },
    stop: function (e, el) {
        $(this).css({visibility : "visible", opacity: "1"});
    },