For Many AJAX is Not Degrading, But it Must
A little over two months ago Chad Dickerson posted one of the most insightful things on his site, Web 0.1 head-to-head: 37Signals' Backpackit vs. Gmail in Lynx. You are saying Lynx? Yes! The point is what 37Signals turns out degrades wonderfully and it is still usable. It could work on your mobile device or on a six year old low end computer in Eritrea in a coffee house or internet cafe (I have known two people who have just done that in the last year and found Gmail did not work nor did MSN, but Yahoo did beautifully).
Degrading is a Good Thing
Part of my problem with much of the push towards AJAX (it is a good, no great thing that XMLHTTPRequest is finally catching on). But, it must degrade well. It must still be accessible. It must be usable. If not, it is a cool useless piece of rubbish for some or many people. I have been living through this with airline sites (Continental), commerce sites (Amazon - now slightly improved), actually you name it and they adopted some where in this past year. In most cases it did not work in all browsers (many times only in my browser of last resort, which by that time I am completely peeved).
When Amazon had its wish list break on my mobile device (I (and I have found a relatively large amount of others this past couple years doing the same thing) use it to remember what books I want when I am in brick bookstores and I will check book prices as well as often add books to my wish list directly) I went nuts. The page had a ghastly sized JavaScript, which did some nice things on desktops and laptops but made the page far too large to download on a mobile device (well over 250 kb). In the past few weeks things seemed to have reversed themselves as the page degrades much better.
Is There Hope?
Chad's write-up was a nice place to start pointing, as well as pointing out the millions of dollars lost over the course of time (Continental admitted they had a problem and had waived the additional phone booking fee as well as said their calls were up considerably since the web redesign that broke things for many). Besides Chad and 37Signals I have found Donna Mauer's Designing usable rich internet applications as a starting point. I also finally picked up DOM Scripting: Web Design with JavaScript and the Document Object Model by Jeremy Keith, which focusses on getting JavaScript (and that means AJAX too) to degrade. It is a great book for designers, developers, and those managing these people.
I have an awful lot of hope, but it pains me as most of us learned these lessons five to seven years ago. Things are much better now with web standards in browsers, but one last hurdle is DOM standardization and that deeply impacts JavaScript/DOMScripting.