[tyler]

So, what the "thread-safe mode" does is enable threads in Rails. (i.e. one thread per request.) To my knowledge, it does not switch out thread-unsafe code for thread-safe code.

Moreover, it's irrelevant. As I mentioned, this is unrelated to why Rails apps are typically run as multiple processes.

[erez]

As with Twitter, I don't think Rails, nor Ruby, is the issue. Whatever you do with a framework, or a language, is mostly your fault. Ruby on Rails can only be as good as the people use it are, and while I realise the Rails aggressive marketing gives people the impression that RoR is a bullet-proof solution, it isn't, and shouldn't be blamed if a developer doesn't understand the tools he's using.