Matt Harrison was talking about making choices between various Ajax toolkits, frameworks, or libraries.
Their survey discusses:
Dojo DWR JSON-RPC-JAVA MochiKit Prototype Rico SAJAX Scriptaculous Xajax Sack
The world of Ajax libs is an interesting one, as they cover various functionality.
We blogged about the Ajax layers in the past:
[Via Ajaxian]I have been doing a lot of backend work with XMLHttpRequest for my Ajax Tagger Version 2, and I am wondering if I should have bothered. I will look into some of these solutions and see what each offers.