It occurs to me that there's really only one feature that would justify the expense of my upgrading from FM10: export to and import from Confluence 4.
Export would allow me to put drafts on the wiki for review, comment, and revision. Import would allow me to bring such revisions back into FrameMaker for release. It would also allow me to import drafts of new documents written by SMEs. (WebWorks ePublisher can publish FrameMaker docs to Confluence 3, but it doesn't work well enough with Confluence 4, which uses XHTML instead of wiki markup.)
