Adam Bosworth – one of the IE designers of XMLHttpRequest, adds some notes of caution
Alex Bosworth – Adams son who describes 10 shortcomings in AJAX
Thomas Baekdal – provides some very well thought out AJAX usability guidelines
Michael Mahemoff – looks at AJAX design patterns, and provides lots of links
AJAXMatters – site devoted to AJAX with list here of AJAX using sites
Jason Gitlin – provides great AJAX intro and error catching at the same time
But the bottom line is that AJAX has re-energized what people expect from a browser-GUI experience (desktop or mobile); laser-focused on the issue of standards compliance within browsers (i.e. Microsofts IE7 team will be in very deeeeeeeppp doo doo if they fail to deliver an updated browser that does not meet current state HTML, CSS, DOM, XML standards or worse, spring a hunk of proprietary code on developers); and really extended thinking on just how big the local browser cache or sandlot is. In sum, AJAX is good news for developers.