[BoB]

$("#tack_portfolio").animate({"top": "+=400px"}, "4000", function() {
   $("#tack_portfolio").hide(0);
});

А в документации написано по другому

.animate( properties, [duration,] [easing,] [complete] )

properties A map of CSS properties that the animation will move toward.

duration A string or number determining how long the animation will run.

easing A string indicating which easing function to use for the transition.

complete A function to call once the animation is complete.