Very amazing stuff. Good write up today, as well. I once thought I should look try to understand at least a bit about Chromium, but then I looked at the codebase. Pretty cool that that stacked navigation takes only 3k LOC.
I think I'm going to switch to exo as user when it's a bit further on. The really like the stacks. I think bookmarks are ripe for innovation, too.
One thing I'm trying to understand is whether this kind of architecture might enable development of better single page applications. A webdocument doesn't know how say a table will get rendered. In other ways on the web there is an abstraction of a document (HTML/CSS) of behaviour (JS/jquery), but not of rendering. My problem is I'm dealing with frameworks like YUI and Ext to create desktop style applications (say a Photoshop or Excel clone). These approaches are really a mess, but I haven't found a way to tackle this. Polyfills and webcomponents are not much of help here.