Déja vu --I’m feeling blue! Unfortunately more and more self-styled pundits seem to be jumping on the AJAX bandwagon, so there's bound ot be a swag of muddled statements coming our way. Pass me the aspirin and anti-nausea pills ...
Luckily there are some more perceptive commentators, and one of these would have to be Yoram Meriaz who has put together what seems (to me) to be an accurate and succinct summary in Back to the Future with AJAX: The Pros and Cons of Replacing Desktop Applications with Web Applications, He looks at the pros and cons of the AJAX methodology and discusses whether or not AJAX is ready for the enterprise.
UPDATE [29 May 2006]:
Just out in AjaxWorld there's a relevant article by Alex Iskold ... The "Webification" of the Desktop: What Are the Implications for Web 2.0 and AJAX? which discusses that "There is no reason why our desktop applications cannot be web-aware."