Pragmatic Programmer Dave Thomas gives us a characteristically pragmatic answer to this question.
So when people ask “should I be using Rails instead of Java?”, the answer has to be “not exclusively: you’re likely to want to use Rails as well as Java.” Why? Because I’m a firm believer in having a bag of tools at your disposal, tools that you know how and—most importantly—when to use. When Rails is appropriate, you’re going to be hard pressed to find a more productive environment.
This is the most thoughtful piece I have read that gives advice on when to use (and when not to use) Ruby on Rails. He also has some really practical advice on ways to introduce Rails in your company.
If you are wondering how (or whether) to introduce Rails in your company, this is a must read.