Guys who designed the LMAX 'disrupter' for Betfair have a good talk about how much trading these betting sites do per second <a href="http://www.infoq.com/presentations/LMAX" rel="nofollow">http://www.infoq.com/presentations/LMAX</a> and how concurrency is a major issue, Erlang makes sense even if they have to search for replacement devs
Kind of light on the tech details, but what with all the breathless "we replaced 8492 Java and Ruby servers with one 386 machine running Go!" pieces, it's worth a look.
i wonder whether they considered scala so they could stay on the JVM (no mention of it in the OP). i don't know Erlang but i develop in scala (w/ Akka) and always interested to know how the two languages are different/similar w/r/t enabling devs to build build distributed systems.