I have been reading a book of the Ruby on Rails framework after 4 years and I've discovered some things that I really like about this framework, bear in mind that I come from a Java world so there are some things that haven't seen in any other Java frameworks.
The migration mechanism is very interesting stuff, not only enables you to make seamless updates on the db it also is fully integrated on the test environment. One other thing to point out is that migration is actual Ruby code so there are a lot of complex things that you can actually do like merging existing DB data to be compliant with any other new changes to the DB.
Another interesting thing is that when developing the "hot deploy" is really great, even if you do major changes to the data model, controllers or flow application there's no need to shutdown the server :).
So far I'm enjoying the Rails development framework for it's simplicity, although I have to say I wouldn't use it for every application, There are lot of frameworks in the Java world that are not only flexible and powerful in their design but also fast on heavy applications.