"Both mutable and immutable sets offer a + method, but their behavior
differs. Whereas a mutable set will add the element to itself, an
immutable
set will create and return a new set with the element added."

This statement is incorrect, + semantics does not change. Example below:

import scala.collection.mutable.Set

val first = Set("A", "B")
val second = first + "C"
println(first)
println(second)

"first" set is not altered.

Listing 3.10 works in Scala 2.7, not in 2.8. Here are the necessary
changes:
import scala.io.Source

if (args.length > 0) {
  // Changes: fromFile now requires a file, not a String; use fromPath
  //          getLines must be getLines()
  //          newline not returned; use println instead of print
  for (line <- Source.fromPath(args(0)).getLines())
    println(line.length + " " + line)
  println()
}
else
  Console.err.println("Please enter filename")

execute thrill.sort((s,t)=> s.charAt(0).toLower< t.charAt(0).toLower) 
gives 
"error: value sort is not a member of List[String]"

should use method "sortWith"

(Based on the Safari version)

The code in listing 3.10 works as-is in Scala 2.9, and the existing
erratum for this page is misleading. Source.fromPath() appears to have
been removed, and Source.fromFile() accepts a single string argument.

Code listed in 3.10 and 3.11 does prints the file in a singleline, and
not as specified in the example in the book. 
The 
print(padding + line.length + " | "+ line)
should be 
println(padding + line.length + " | "+ line)