There are two types of slow: there is slow to react, and slow to respond. I can understand that IntelliJ is having a hard time recompiling the Scala source. As you said, Scala is difficult to parse and compile.
What I don't like is the context menu taking several seconds to even appear, locking up the entire UI (!), when I right click. Or music playback going haywire just because I am switching files or refactoring. Setting it to "low priority" solves that last issue, but that doesn't make me feel better about IntelliJ.
If an app is slow, fine. But deal with it. React quickly, respond later.
PS: I say that now, but once I have a better computer, it's all "IntelliJ is great." I only feel this way because my computer can't take it.
Oh, and on that note, that wasn't the only reason I left IntelliJ. I also disliked how it handled having multiple projects open. If you don't want everything in separate windows, IntelliJ makes you create a dummy project and import everything as modules. NetBeans just does what I want automatically.
Where does the POM specify the project specific code formatting you want to use?
Where does the POM specify the exact JVM flags and params given to various launch configs?