Blaine Cook, formerly of Twitter, reminds folks that architectures scale, not languages.
Some folks have been complaining recently that RoR doesn’t scale, yet sites like Yellowpages.com know how to do architecture and do just fine with it. This isn’t to say that Ruby and Rails both couldn’t be faster and better optimized for scaling, but ‘going wide’ should be easy with a good architecture.
The claim of request uniqueness in Twitter’s case is an illustration of an architecture challenge. I’m always amazed how well Slashdot does with that same problem.