I am still working on the development of AJAX Tagger 2. Currently I am developing a little framework that will help me query datasources.
I have developed a priority queue for AJAX Requests. There are 5 queues and work is delegated between the queues based on the need of the request. An urgent request will get placed in the queue that cycles the fastest, a non-urgent request will get placed in a queue which only cycles every once in a while.
Take a look at http://www.kinlan.co.uk/AjaxExperiments/AjaxTag2
, and you will see the tags are requested on a priorty queue and the tag stats are requested on a slower "thread".
All the page is completely async! :)