Say I'm a Python developer and I'm looking to write services that are fast. Would I likely be better off going down the route of node.js, Go, Haskell, Erlang? I mean they are all fantastic languages and I've dabbled in most of them but from what I've read, Go seems to be the best one to use if you don't want to shake your world up, but if you do, Haskell or Erlang are nice new paradigms to dive into. Is this true?

Erlang has decades of use in fast, robust, large telecommunication systems. Haskell promises more robustness than any other platform as well as performance sometimes comparable to C. Its downside is just that steep learning curve though.

So if you want speed, I'd go for those two out of your list. Go and node.js are still infants in the game, so I don't think there is enough serious software out there built with these to properly judge their effective speeds.

- Google is using it internally, where speed is an absolute requirement

- Vitess, recently open sourced (and used internally by youtube) would definitely have to be fast for the task youtube is using it for. (http://code.google.com/p/vitess/)

- Desktop window manager in Go that is very fast even on lower spec machines: https://github.com/BurntSushi/wingo

Just my two cents. I would absolutely stay away from node.js if you are in an environment where people touching the code aren't easily accessible, since it's very easy to write javascript that only you understand. The other languages seem to punish it a bit more, while at times it feels as if javascript embraces it.