[doktrin]

This. That said, since the OP is already a developer I would think he has sufficient base to dive into a RoR project should he desire.

Perhaps if his domain were radically different (say, embedded systems) he would need to explore the fundamentals of web application architecture before putting together a rails app.

That said, I still remain on team "learn the fundamentals", and have yet to find a truly compelling reason to take the "grok as you go" approach. Maybe I'm just stubborn.