I just posted a new article in the JSClasses blog site that tells a bit about AJAX and the XMLHttpRequest object and the most important new features of the level 2 specification as well other related specifications like HTML 5, File API, Cross Origin Resource Sharing, which will help you taking your AJAX applications to the next level.
While you are reading this, I just would like to comment that the PHPClasses and JSClasses blogs are open to submissions of interesting posts about PHP and other related subjects of interest of all Web developers in general. It can be a general interest article or about an Open Source project (not published in the PHPClasses or JSClasses sites already) that you may have and would like it to get a good exposure boost.
I have already received a few articles, some are still being evaluated but others were not accepted because they were too superficial or irrelevant for Web developers. So, if you would like to publish here an article but you are not sure if it would be relevant enough to be accepted, feel free to contact me sending a message to info at phpclasses.org.