I have been a big proponent of XForms withn the TSSG (though I haven't yet convinced our commercial development teams to deploy solutions based on X-Forms).
2006-03-14: XForms 1.0 Second Edition Is a W3C Recommendation.
The World Wide Web Consortium today released XForms 1.0 Second Edition as a W3C Recommendation. The new generation of Web forms, XForms separate presentation and content, minimize round-trips to the server, offer device independence, and reduce the need for scripting. This second edition adds clarifications and corrects errors as reported in the first edition errata. Second edition publications include the following documents.
This is a good overview article on the subject Why XForms Matter, Revisited - O'Reilly XML Blog