Web technologies in GUI apps

What's your experience in using web technologies (HTML, XML, CSS, JavaScript) to implement part of the functionality of a GUI application? Pros and cons, please.

No servers, relational databases, AJAX, or cookies for session management, nor an existing webapp either, but rather a GUI app that uses web widgets (like Qt WebKit) to render and handle substantial parts of the UI, while taking advantage of a GUI framework to achieve an even richer interaction and better desktop integration.

I've already validated that the approach is possible using PyQt. Content can be rendered from the file system or from strings, and URL requests (images or clicks) can be captured and served by the form's event handlers. CSS and JavaScript are supported, perhaps with some limitations.

        # ...
        self.webView.page().setLinkDelegationPolicy(
            QtWebKit.QWebPage.DelegateExternalLinks
            )
        #... 

class TotiMainWindow(QtGui.QMainWindow):
    def linkClicked(self, url):
        pass # events arrive here

Note: This question is different from this one and this one made before, among other things because there is no requirement to use web technologies on the GUI, but there is the requirement that the application should work without a network connection available, and should integrate well with the default desktop over different platforms, without previous infrastructure requirements (no .NET, Java, browsers, or database servers).

Note: I posted a different version of this question on PMS but found very little experience with this approach there.

Closing Note

I just found most of the information I was looking for in a series of blog posts by André Pareis.

Solution

We did exactly this for a project back when Windows XP was new.

This gave my team several benefits:

A good-looking UI with relatively little effort
Easily change the style of the UI in a consistent manner using CSS
Relatively simple integration with C++ (invoking functions from the ui and vice versa)

The drawbacks we saw were:

Some not-so-good firewalls considered accessing internal resources (ie other html pages in the ui) to be a web request
Adding and accessing the needed resources could in some cases be a bit cumbersome
It was possible set properties in Internet Explorer that would prevent JS from running in the application

Note that some of Windows XP:s programs are using this approach.

This probably works best with small, more Wizard-like parts of the ui (which our ui consisted almost entirely of).

I have since then not really been involved in ui projects, so I cannot really tell you whether this approach is still valid... I know that MFC-based applications will let you use HTML-based dialogs though.