I was working with Erlang for about 2 years in a multi-language environment, and we based our networking messaging infrastructure on top of the Erlang protocol. It's still there, but we're migrating from it.

One major thing that turned me off of the language for our particular project was that there was no way to have a large read-only data structure in RAM and sic a bunch of parallel threads to analyze or search it. It is hackable if you mash your data structure into a large byte binary, since large bins live on a shared heap, but it's a pain to deal with non-native representation for your data.

It's very obvious that Erlang is optimized for a particular usage model, and even when you're dealing with a number of functional parallel processes, it might still clash with what you're doing.