some points about RoR, (I checked it a few months back so they might have changed!)

- It does not offer an out of box solution to allow authenticated users to create content forming pages as part of a Web site. It offers you a web app framework and you could build upon it your custom CMS from scratch (and it will take you longer to do so)

- but there is a nice binding to the database through the framework

- at the time stability was a bit of an issue!

with all that said there are great applications built upon it such as 37Signals Base Camp