Small sample of reasons why the Scala standard library (especially collections) might need rewriting (many taken from Paul Phillips talks on the Scala Collections library):
scala> List("a", "b", "c").toSet // the only reasonable line of code in here
res1: scala.collection.immutable.Set[String] = Set(a, b, c)
scala> List("a", "b", "c").toSet() // seen this when learning Scala first time. ROFL.
res2: Boolean = false