Is there a jQuery add on that has slideUp and slideDown effects with damper effect? That is, the change of size starts with a rather quick speed, and slows down towards the end of the movement.
You can pass in an easing to use as a second argument...
$("#something").slideDown(500, "linear");
jQuery includes swing and linear, with the former being the default.
To get the behaviour you describe, use easeOut, which is available in jQuery UI (which you've tagged the question).