First of all, I don't think it's fair to accuse the Twitter dev team of working without real experience and numbers to back up their decisions. They have a huge volume of data being generated by their service, and have weathered the whole "Rails doesn't scale" flame-fest with relative grace and good humor. IMHO, that entitles them to talk fairly freely about the relative scalability of different languages and frameworks.

Secondly, any "ranting" you hear in this article is the product of El Reg, not Alex. He mostly offered a calm, positive presentation about the improved speed (with relatively little, if any, tradeoff in developer productivity) that came from using Scala instead of Ruby for critical infrastructure services.

Regardless, most Java web applications' performance issues stem from framework-itis, not from the underlying runtime. By itself, Tomcat (or another modern Java servlet container) is capable of some pretty impressive throughput -- perhaps not on par with a lean, pure C server like nginx, but not nearly as limited in functionality and extensibility, either.

No matter what you think about Java the language, you at least have to admit that HotSpot blows MRI, YARV, the Python VM, and Parrot out of the water when it comes to raw performance on low-level code. That doesn't save you from bad implementation ideas, but it does at least give you the possibility of getting fast, efficient code, if you have a decent compiler and work fairly close to the metal.

Using Scala is one way to produce that sort of low-level implementation code without wanting to gouge your eyes out (which is how most Java source tends to make me feel, anyway).