Answer by fehays for Mouse position relative to div

Take a look here:

http://docs.jquery.com/Tutorials:Mouse_Position

EDIT: The jquery docs page above is broken. Here is an alternate:

http://api.jquery.com/event.pageX/

event.pageX and event.pageY should give you mouse position

$("#drag").draggable({
    stop: function(event, ui){
        var x = event.pageX - ui.offset.left;
        var y = event.pageY - ui.offset.top;       
    }
});

EDIT: here's an example showing how to track the mouse position relative to the element you are dragging http://jsfiddle.net/87fqr/1/

ANOTHER EDIT:

This should work if you want the position of the mouse relative to the droppable:

$("#db_tables").droppable({
    activeClass: "ui-state-default",
    hoverClass: "ui-state-hover",
    drop: function( event, ui ) {
            var offset = $(this).offset(),
            x = event.pageX - offset.left,
            y = event.pageY - offset.top; 
        $('<div style="margin-top:' + y + 'px; margin-left:' + x + 'px; "></div>' ).html( ui.draggable.html() ).appendTo( this );
    }
});

More complete example here: http://jsfiddle.net/87fqr/2/