When this talk comes from a Twitter developer, who loves both Ruby and Rails and happen to be running probably the most punished RoR site on the Internet right now, I’m inclined to believe. (they’re taking over 11,000 requests per second during peak times). Here are a few quotes from the interview:

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.
It’s also worth mentioning that there shouldn’t be doubt in anybody’s mind at this point that Ruby itself is slow. It’s great that people are hard at work on faster implementations of the language, but right now, it’s tough.

[ Link: Interview With Twitter Dev ]

Does this discourage me from Ruby or Rails? Hell no. To me the elegance of the language completely dominates its flaws, especially when you realize that there exists a small legion of very smart people who are obsessed with fixing these problems.

No, I’ll be sticking with Ruby and Rails. I’ll wait for the performance and scale issues to be fixed in subsequent releases. The language/framework is too beautiful to shun.