Related link: http://www-128.ibm.com/developerworks/java/library/wa-ajaxintro2/index.html
IBM has posted part 2 of their Mastering Ajax series. The great thing about this tutorial is that it walks you through the basics of Ajax development step by step. Check it out if you are interested in one of today’s biggest buzzwords!
too informal, too long
That tutorial has a lot of useless chatter and has no information that has been available on the Apple site (http://developer.apple.com/internet/webcontent/xmlhttpreq.html) for about a year (give or take).