I came across a great post on the IDEA Scala Plugin message board the other day. Apparently there are best-practices/conventions for writing method signatures in Scala. Adhering to these rules communicates to the user more than just argument and return types: it can tell you if a method has side-effects, or is meant to be a "property".
Check it out: Rules for Scala method signatures.
Also check out IDEA 10: the best Scala IDE.