A few interesting quotes:

All the convenience methods and syntactical sugar that makes Rails such a pleasure for coders ends up being absolutely punishing, performance-wise.

It’s also worth mentioning that there shouldn’t be doubt in anybody’s mind at this point that Ruby itself is slow.

All of us working on Twitter are big Ruby fans, but I think it’s worth being frank that this isn’t one of those relativistic language issues. Ruby is slow.

Ruby is a great language, but this is just further proof that you need to take a close look at your requirements up front, then pick the best (not necessarily the coolest) tool for the job at hand.