cybercool

take a look on http://plugins.svn.ww.wp.xz.cn/jquery-smooth-scroll/trunk/js/jss-script.js

// Scroll to top speed
	var scrollSpeed = 500;

and

$(scrollElem).stop().fadeTo(300, 1); // fade back in
		}else{
			$(scrollElem).stop().fadeTo(300, 0); // fade out