As I said, I avoided JS and only used it for simple one-lines that could do something I could not easily do any other way -- and only "things" that would not detract from the experience if JS was not available on the user's end.
Since AJAX depended on JS and I also considered AJAX too complex to code (not "difficult", just requiring too many disciplines, (HTML, JS, CSS, DOM and a back-end scripting language), I avoided it also.
This year I embraced both.
The best argument I saw for using AJAX was a simple link on an eBay page. For years, I would do complex searches on eBay and save them as "Favorite Searches".
To save a search required:
1. click the "Save this search" link
2. be taken to a separate page with options, (e.g.- recieve emails when new items matches the search, give the search an easy to remember name, add a note).
3. After saving, I was taken to "My eBay" searches page where I would click the newly created search to get back to where I was before step 1.
One day, I hovered my mouse over the "Save this search" link -- deciding if I should save it or not....
After a few seconds, a CSS hidden div appeared with the form to save the search -- I completed the form, clicked save, and the div disappeared.
Not only had my user experience been greatly improved, but eBay just saved thousands of bytes of data transmission by not having to display (4) complete pages. (And the "Back button" issue made no difference at all -- in fact, I was glad that it still brought me back to the page I was on previous to saving the search).
As a programmer, (and someone who used to write a lot of offline ".EXE" type applications), I find it simple to pop an Ajax window open and display a small bit of data, rather than repaint the entire screen and interrupt the application flow -- the bandwidth reduction is just icing on the cake.
..also on the AJAX "Back Button" issue -- if you watch average users interaction with a browser, you'll find many don't use the [BACK] button at all -- they expect to find all navigation on-site and in the viewport.