Coda Hale is Yammer's infrastructure architect. Yammer is moving their infrastructure code from Scala to Java. Typesafe's CEO (the company founded by Scala's creators) asked him for his reasons and his email was made public by mistake. Read more here
I've worked for 2 years now in on a complex scalable service exposed via web-service created in Scala and my experience was very different. Here are my thoughts.