Came across this site while reading AJAXIAN.
Basically, it's a benchmark on different AJAX method.  It measures the usage of bandwidth and execution time.
So far, for pure AJAX, looks like it's AJAX using JSON serialization is the best choice.
For those using FLEX, FLEX using AMF3 serialization is your best bet.

This is a great way to mash up different web content together (web service, RSS, etc.).
Think Linux / PowerShell pipe mechanism (i.e. ls | grep shoot | more) for web content.
Try it out here.
Here is a good webcast of it.