Andrew Carter has an interesting piece on Radiant CMS on Rails.
The state of cms/blogging software on rails is still weak. Maybe it is because of what Andrew said, that it is so easy to build a cms in a couple of hours. But still I think the RoR community should go with one and strengthen it. Something like mephisto, typo, or radiant could be great contenders to wordpress if their roadmaps got more serious, thus pulling in greater community support.