Good non-answer.

For many large, non-trivial systems have several requirements: - tends to have complex dependencies - needs fast builds

This was a classic: http://www.amazon.com/Large-Scale-Software-Design-John-Lakos...

Essentially how to design C++ systems so that incremental compiles don't sink you. Developer productivity is important.

Scala is badly failing on this front IMO, it reminds me of the old bad days of C++ in a major way.