Looking at the Actor tax for simple I/O bound operations. With actors it takes ~1000ms. Without it takes ~450ms.

charcount.scala

package com.postneo
package toys
package charcount

import scala.actors.Actor
import scala.actors.Actor._
import scala.io.Source

// Iterate over lines in a file, summing the total.
object CharCount {

    def main(args: Array[String]) = {
        var totalChars: Int = 0
        val startTime = System.currentTimeMillis
        for (line <- Source.fromFile("/usr/share/dict/words").getLines) totalChars += line.length
        println(totalChars + " chars total")
        println(System.currentTimeMillis - startTime + "ms")
    }
}

// Classes used for messaging to the actor
case class Line(line: String)
case class Stop(startTime: Long)

// An actor that reacts to either Line or Stop messages, summing the total as it goes.
class Counter extends Actor {

    var totalChars:Int = 0

    def act() {
        loop {
            react {
                case s:Line => {
                    totalChars += s.line.length
                }
                case s:Stop =>  {
                    println(totalChars + " chars total")
                    println(System.currentTimeMillis - s.startTime + "ms")
                    exit()
                }
            }
        }
    }
}

// Iterate over lines in a file and send messages to an actor for totaling.
object ActorCharCount {

    var counter: Counter = new Counter

    def main(args: Array[String]) = {
        val startTime = System.currentTimeMillis
        counter.start
        for (line <- Source.fromFile("/usr/share/dict/words").getLines) counter ! Line(line)
        counter ! Stop(System.currentTimeMillis)
    }
}