At my company we started a Scala project a little over a year ago. Two of us had a Java background the other two had a C++ background. We targeted Scala 2.9,

At my company we started a Scala project a little over a year ago. Two of us had a Java background the other two had a C++ background. We targeted Scala 2.9, Akka 1.3, and ran it on JVM 1.6. For us the stack proved to be very easy to work with. The project spent about 5 months in development and has been in production for another 9 months with weekly updates. What the author calls old habits, I call productivity. A lot of us started off coding imperatively and slowly started adapting functional along the way. It allowed us to get the best of both worlds. Over the past year we've definitely stumbled a few times (mutable objects for akka messages are really really bad), but overall we've been very happy with the stack. One of the only real ongoing problems we are continuing to struggle with is limiting the impact of big GCs in production. Scala tends to generate more garbage then pure Java, so the GC has to work harder. Most of these objects are in the eden space, but we can run into memory fragmentation issues, which leads to eventual long compaction cycles.