In Scala 2.8, the actors package has been revised and extended. The new Scala Actors API overview [1] introduces the types and members that have been added. At the same time, it provides in-depth documentation (from a user's perspective) for large parts of the package that already existed in previous releases.
Links:
[1] http://www.scala-lang.org/docu/files/actors-api/actors_api_guide.html#