Real World Problems with Ruby on Rails
This Q&A with a member the TWITTER team shows that Ruby on Rails (RoR) is not, at this point, a scalable technology. The language itself is show (can be solved) and the reflection based idioms are also slow (could be solved with machine code generation, I suppose) and it's ability to scale out has limitations.
Microsoft is building a CLR-based Ruby implementation, IronRuby, which should be a lot quicker than current implementations. But this damning comment from the Q&A makes one wonder whether an enterprise should bet on this technology:
Once you hit a certain threshold of
traffic, either you need to strip out all the costly neat stuff that
Rails does for you (RJS, ActiveRecord, ActiveSupport, etc.) or move
the slow parts of your application out of Rails, or both.