This is what I love about Ruby and Ruby on Rails, once you learn the basics of Ruby and how a RoR app is put together you can use this knowledge to learn about other technologies, in this case Facebook Applications. The reason for this is, as soon as a new technology hits the street somebody is bound to either build a Ruby library or a RoR plugin targeting the new (and presumably cool) platform. In two excellent articles Stuart Eccles shows how to build a Facebook app using the rFacebook Rails extension. I guess I could have looked at a PHP or Java example but I chose (as I nearly always do) the Rails route as the layers of abstraction and the standard infrastructure of RoR apps allow me to quickly get an overview of the new technology in action but also, if I so desire, allow me to easily deep dive into anything that requires more detailed investigation.
In the late nineties I learned Java (and later .NET) for a similar purpose not as a primary development tool but because of its role as the “language of account” of most new technologies at the time. And although I still come across environments where the only examples are in a Java (or .Net or PHP) I know if I wait a few weeks some bright Rubyist will eventually “document” it in either Ruby or Rails.