Scala is slow to compile. This was exasperated for me by the fact that I had just finished spending 2 weeks working in Go (which compiles stupendously fast) before trying scala.

I don't understand people who can put themselves through that much pain. FSC doesn't come close to addressing it well enough. I think anyone who's used to the compile-free nature of dynamic languages is going to have a hard time with Scala until it's resolved.