I have built the backend (game logic and comet) for http://www.iluminatus.ro, a trivia-like multiplayer game for the Romanian market. We're going to release an english version soon.

It was a great fit. It lacks Unicode processing capabilities by default, but there are a few open source libraries for that. The only thing I dislike about Erlang is the poor string manipulation and lack of clean structures (Erlang's records are an ugly hack IMO).