Making AJAX navigation optional

I just put up a proof of concept for the AJAX chapter of my book. For years I have ranted about DHTML multi level menus simply assuming that every user wants to have every page in the sitemap as an item in the navigation.

My idea was to make the enhanced navigation optional and allowing the user to decide initially.
Check out the example:

• Optional AJAX navigation

It uses PHP to only provide a chunk of the full navigation automatically replacing the current link with a strong when JS is unavailable and when JavaScript is available it offers a link that turns the navigation into a multi level tree menu loading the main page content via XHR.

What do you think? Helpful? I think it is a lot less obtrusive than a lot of fancy menu systems out there while offering the same options.