Dubinko has done a ton of great work and I admire what he's put together with XForms, but I just don't think his response does anything to discredit what Ian had to say. Until there's a large outcry from developers to support XForms, there's going to be no effort made to integrate within the browsers. I know there's a few diehard XForms fan, but we're a long ways away from the mass of developers being ready to use and understand XForms.
One point I really disagree with Micah on is the trusting of XForms to do server-side validation. There's no way using HTTP that I place any trust in an response received from the client. It's way to easy for someone to arbitrarily change the rules of the XForm when they submit the document back to the client. You really still need to do something on the server end of things to verify the "signature" of the XForms. After verifying the signature of the document, you'd still need to re-validate the data in the form. So, it's not as simple as he stated in his response.
On the good news, I know there are a ton of companies working to integrate XForms into their products, so that should help increase XForms exposure and get developers familiar with the concept. I know I've even been working on some very specialized XForms to qForms XSLT documents. :)