To summarize: Drupal and Rails are each good for different types of webapps and different development styles. Sometimes Drupal will be the right tool, sometimes Rails will be it, other times neither is good.
I think they are very different tools. With Drupal you have a product ready to use, which does certain things. With Rails, you have a set of tools (great tools) to start building a certain thing. With Drupal you can have a site up and running in 5 minutes; with Rails you have to build your site from scratch (although building it its fast). So that leaves apart from Rails many people who hasn't the time or the knowledge. Expect to see a Drupal-like built in RoR in the future. The phylosophy of Rails (or its creator) is to build the framework, but never offer a general-purpose solution for certain problems, because every implementation is different and reusable components are a myth; ie, you will never see a poll module or a blog module built in Rails. álvaro