There's lots of case studies on akka in production, and people using are generally happy but also honest about bottlenecks they hit (more than a few thousand messages in message box etc

http://www.addthis.com/blog/2013/04/16/building-a-distribute...

http://marakana.com/s/akka_hammer_scala_nails,1129/index.htm...

http://corp.klout.com/blog/2012/10/scaling-the-klout-api-wit...

http://blog.kreuzverweis.com/uncategorized/moving-from-osgi-...