Added Ian Eure's (atomized.org) Drag and Drop code to the repository, for further testing.

drag/drag.js

+$.drug = null;
+
+$.dragstart = function(e)
+{
+    this.dragElement.deltaX = e.clientX - this.dragElement.offsetLeft;
+    this.dragElement.deltaY = e.clientY - this.dragElement.offsetTop;
+
+    // Save CSS
+    this.dragElement.oldPos = $.css(this.dragElement, 'position');
+    this.dragElement.oldCursor = $.css(this.dragElement, 'cursor');
+    this.dragElement.oldUserSelect = $.css(this.dragElement, 'user-select');
+
+    $(this.dragElement).css('position', 'absolute')
+                       .css('cursor', 'move')
+                       .css('user-select', 'none');
+    $.drug = this.dragElement;
+};
+
+$.dragstop = function(e)
+{
+    $.drug = null;
+
+    // Restore CSS
+    $(this).css('cursor', this.oldCursor)
+           .css('user-select', this.oldUserSelect);
+}
+
+$.drag = function(e)
+{
+    if ($.drug == null) {
+	return;
+    }
+	
+    // Update position
+    var nx = (e.clientX - $.drug.deltaX);
+    var ny = (e.clientY - $.drug.deltaY);
+
+    // Bounds check
+    // Left edge
+    nx = (nx < 0) ? 0 : nx;
+    // right edge
+    nx = (nx + $.drug.offsetWidth) > document.width ? document.width - $.drug.offsetWidth : nx;
+
+    // Top
+    ny = (ny < window.scrollY) ? window.scrollY : ny;
+
+    // Bottom
+    ny = (ny + $.drug.offsetHeight) > window.innerHeight + window.scrollY ? window.innerHeight + window.scrollY - $.drug.offsetHeight: ny;
+            
+    $($.drug).css('left', nx + 'px')
+             .css('top', ny + 'px');
+};
+
+$.draginit = false;
+
+$.fn.Draggable = function(handle)
+{
+    // Don't add > 1 of these handlers
+    if (!$.draginit) {
+	$(document).bind('mousemove', $.drag);
+    }
+    
+    return this.each(function()
+    {
+	var dhe = handle ? $(this).find(handle) : $(this);
+	dhe.get(0).dragElement = this;
+
+	dhe.bind('mousedown', $.dragstart)
+	   .bind('mouseup', $.dragstop);
+    });
+};