Using XML to Move Past Forms

XForms The W3C is working on a standard for a next generation of XML-based forms, which can then be integrated with XHTML and other XML-based vocabularies.
Patent issues? Shana appears to have a patent which may apply to XForms and several related XML technologies.
XML as MIME-compliant rich format You can use existing text areas and file attachments to send XML from the client to the server, though the interfaces aren't especially beautiful.
Learning from the protocols XML protocols are already using technology built for HTML forms to ship XML documents around the Internet.