Caching CORS, Cache poisoning and the Vary HTTP header Understanding the Vary header is key ensuring CORS will work with CDNs and caching.
Drupal High performance AJAX callbacks with Drupal 7 and the JS module Make lightning fast AJAX queries in Drupal 7
Drupal Attaching AJAX events to non-form page elements in Drupal Making AJAX request in Drupal using the form API is real nice and simple