Well said, extensive use of AJAX, that reminds me years ago when java is the big word, they try to do everything in java, Corel even try to build an office-like application out of pure java, but as I remember it turns out to be a failure somehow...
I think a website should be considered as a publication and we should rethink the position of php,javascript,html,css in the process of creating this publication...
Also, seperating presentation with logic doesn't mean that we need to have yet another template engine. We can
1. let a designer do the template prototype first (more from a visual point, I found designers really like photoshop)
2. a html/css coder put this prototype into html template and even better design a good style sheet for that
3. a php (or perl, ruby... what ever) coder figure out how to generate server side code to generate pages based on the templates in step 2
Clear-defined roles sometime is more important...
Also, I found many of the CMS(System/Framework, more to me as website pulishing system) out there are pull-based, data pulled from database, with website as a publication in mind, such system should be push-based, generate pages from database... doing that we can even avoid using the ugly mod_rewrite/pathinfo tricks to generate search-engine friendly urls...
There's an article talking bout this:
http://www.sitepoint.com/article/push-pull-best-cms which i think is very good...
--Jim