The second for loop will never be evaluated unless links in explicitly resolved, eg val nl = links()...

gistfile1.scala

package com.test

import dispatch._
import scala.collection.JavaConverters._

import java.io.{ FileOutputStream, File }
import org.apache.commons.io.IOUtils
import scala.concurrent.ExecutionContext.Implicits.global

object App {
    val URL = "http://flickr.com/explore"

    def mkUrl(u:String) = url(u)

    def wrOut(ab:Array[Byte], nm:String):Unit = {
        IOUtils.write(ab, new FileOutputStream(new File("/tmp/" + nm)))
    }

    def fetchByte(u:String) = Http(mkUrl(u) OK as.Bytes)

    def main(args:Array[String]) {
        println("starting...")
        val reqf = Http(mkUrl(URL) OK as.jsoup.Document)
        val links = for {
                req <- reqf
            }
            yield req.select("img[src$=.jpg]").asScala.toList

        for {
                lel <- links
                ts <- lel
            } {
                val nm = ts.text
                println(nm)
                val link = ts.attr("src")
                val nr = fetchByte(link)
                for (r <- nr) wrOut(r, nm)
        }
        println("nothing was evaluated...")
        Thread.sleep(5000)
    }
}