There seems to be an animate bug with jQuery 1.2. Try animating the css left value of a relatively or absolutely positioned element. For instance, I have an object with a css left value of "-880px". When I call .animate( {left:"-1760px"} ,300, function(){ alert( $ (this).css('left')}), the callback will result in "-2640px", not "-1760px" like it should be.
The above code worked in version 1.1.2, not 1.2.