Here a nice Ajax sample using jQuery and ajax calls to render the tree and internal module code.
All this is done using the component : Module Extender.
If you look in Firefox console or google Chrome, the tree display and the code itself take approximately 200 ms in ajax but the total page render more then 2 Secondes in case of full page reload.
(10 x the time compared to ajax call). All the advantage for Ajax call.
You can make an endless queue using ajax (facebook,disqus,google use it in many case today) to speed up your page and item loads.