From the XML-DOC list:
That said, I do think most XML editing tools are pretty awful (and if you don’t spend the time to make them useful for your content model, they are even more awful – but that’s a problem for the implementer) – they just about work when you’re editing existing content but almost all of them are really annoying when doing content creation.
Building useful XML editing tools for non-gearheads remains a difficult problem, and I’m wondering if document authoring will end up going to variants of DITA, DocBook, Open Document, and plain-old XHTML, abandoning custom schemas and DTDs out of exhaustion.
ETA: the Dojo Toolkit people have a working in-browser editor.