Of all the journaling sites, Dreamwidth has the best support for OpenID. Dreamwidth allows users to log into their site, using their LJ/IJ/JF id. They can upload six icons, view and comment to entries, join communities, and add/be added as a friend (though the terminology of friending is different, please note). This means that you don't actually need to join DW in order to participate in their communities - you only need to create an account if you'd like to post entries of your own.
So I can log into DW's site using my IJ information, and post on topics there? Is the only reason to get a DW account to start threads/entries and not just comment on them?