Nothing real special. The AJAX loading icon can be changed using the Javascript variable ajax_load_icon in header.tpl.
// UK lang variables
tinyMCE.addToLang('layer',{
insertlayer_desc : 'Insert new layer',
forward_desc : 'Move forward',
backward_desc : 'Move backward',
absolute_desc : 'Toggle absolute positioning',
content : 'New layer...'
});