We used Scala in production at my previous job. It was great for the most part, but upgrading from 2.9 to 2.10 was a massive, massive pain. I think I spent nearly a week on the refactor. We didn't even have that much code (relatively speaking); the majority of the time was spent on finding substitutes for the libraries which were irreparably broken, and rewriting client code against the new API. That's pretty damning, but we could have avoided the upgrade if the team had better communication, so I see this also partly as a human issue.
That being said, I would be willing to use it again. I didn't have an issue with compilation speed, and the size/flexibility of the language wasn't really a problem; we wrote in what I believe is the idiomatic Scala style (immutable objects, FP). Going back to Java now, I SORELY miss lightweight lambda expressions, pattern matching, native Option type (that people actually use), and the emphasis on immutability.
That being said, I would be willing to use it again. I didn't have an issue with compilation speed, and the size/flexibility of the language wasn't really a problem; we wrote in what I believe is the idiomatic Scala style (immutable objects, FP). Going back to Java now, I SORELY miss lightweight lambda expressions, pattern matching, native Option type (that people actually use), and the emphasis on immutability.