quick overview of extending jQuery UI widgets in 1.8 and 1.9

1.8.js

(function( $, prototype ) {
	$.extend( prototype.options, {
		spinner: "<em>Loading&#8230;</em>"
	});

	var _create = prototype._create;
	prototype._create = function() {
		_create.call( this );
		var self = this;

		this.element.bind( "tabsbeforeload", function( event, ui ) {
			if ( !self.options.spinner ) {
				return;
			}

			var span = ui.tab.find( "span" ),
				html = span.html();
			span.html( self.options.spinner );
			ui.jqXHR.complete(function() {
				span.html( html );
			});
		});
	};
}( jQuery, jQuery.ui.tabs.prototype ) );

1.9.js

$.widget( "ui.tabs", $.ui.tabs, {
	options: {
		spinner: "<em>Loading&#8230;</em>"
	},
	_create: function() {
		this._super( "_create" );
		this._bind({
			tabsbeforeload: function( event, ui ) {
				if ( !this.options.spinner ) {
					return;
				}

				var span = ui.tab.find( "span" ),
					html = span.html();
				span.html( this.options.spinner );
				ui.jqXHR.complete(function() {
					span.html( html );
				});
			}
		});
	}
});