It amounts to "Scala is too complex, ugly and slow to compile."
Yammer moved from Scala to Java BTW: http://blog.joda.org/2011/11/real-life-scala-feedback-from-y...
My ideal language would be some mix of Kotlin, Ceylon, Dart and Julia.
Some examples: Twitter, LinkedIn, Foursquare. All of them pretty big and in the same space of Yammer; they seem quite happy and don't plan to move away from Scala.
And here you can find a clarification from Yammer about that issue: http://eng.yammer.com/scala-at-yammer/
TL;DR: They liked Scala but it has rough edges, every programming language has rough edges (yes, including Java). They found Scala was not the best option for some particular situations and Java was a better fit. End of story.
That's fine and completely reasonable, I think nobody said Scala is the Holy Grail in programming languages. As for your preference, you seem to be looking for a "nicer than Java, but OOP all the way" (don't know about Julia, haven't used it), which is OK as a preference but many of us find it a kludge to work with. I found something like Scala (multi-paradigm, I mean) helps me a lot in reasoning about code. As I said, you use the paradigm that makes more sense.
For complexity and ugliness, you have my previous answer. About compile time, you have a sophisticated type system and type inference which come at a cost, but it's not such a big deal when you run it with fsc (which stands for fast scala compiler).