Perhaps this "rethinks the CMS" from a performance perspective, but it certainly doesn't rethink the CMS from the end-user point of view -- they still need to manage content using an admin area that is different than the front-end of the site (thus breaking their mental model of what the website is and how it works).
If you want to see a CMS that rethinks the end-user interaction, take a look at Concrete5 -- http://www.concrete5.org/ (built in technically boring but easy-to-deploy-on-cheap-hosts php), or Webvanta -- http://www.webvanta.com/ (closed source so not sure what it's built in).
I have found it much easier to train non-technical clients who don't already have blogging/wordpress experience with Concrete5 than any other CMS I've used in the past.
I actually dislike in-place editors. As a writer of posts, I actually prefer to edit and write text outside the context of a webpage. There's too much visual distraction - images elements, ads, columns, etc that end up cluttering the editing workspace. Concrete5's model of using overlays also screams distraction to me. Why not just use a clean admin interface? It's also better for professional writers who don't need to know the minutia of which column and which part of the site the text is going into.
Concrete5 might be easier for people who want to build websites, but in-place editing just doesn't work for people who only want to write and put together actual content.
True -- a dedicated writing interface makes much more sense for blog where you are adding new content that is similarly-formatted on a daily basis. But if you're building a marketing or informational site for a business, a traditional CMS makes a lot more sense.
fyi, Webvanta is built with Ruby on Rails, and a bunch of other stuff... It is a designed as a SaaS system and uses a cluster of servers running various things (nginx, clustered MySQL, and a few others). As noted above, there's some more details on the technology we use at www.webvanta.com/technology.
If you want to see a CMS that rethinks the end-user interaction, take a look at Concrete5 -- http://www.concrete5.org/ (built in technically boring but easy-to-deploy-on-cheap-hosts php), or Webvanta -- http://www.webvanta.com/ (closed source so not sure what it's built in).
I have found it much easier to train non-technical clients who don't already have blogging/wordpress experience with Concrete5 than any other CMS I've used in the past.