I recently used the activemenu module in a project. Thanks to the maintainers who put this code out in the community to make it available. I tried to distill some of the challenging aspects into the web-page http://palma-seo.com/content/using-jquery-json-and-ajax-drupal so feel free to take a look at my experience there. You can see the finished product at (for instance) http://www.rockpeaks.com/shows/r/Rockpalast at the bottom in the "Clip List". I also did a screencast at http://www.youtube.com/watch?v=UBKv5HxwJ18 that you might find interesting.