Why boxing doesn't keep me awake at nights

I'm currently reading the (generally excellent) CLR via C#, and I've recently hit the section on boxing. Why is it that authors feel they have to scaremonger about the effects boxing can have on performance?

Here's a piece of code from the book:

using System;

public sealed class Program {
   public static void Main() {
      Int32 v = 5;   // Create an unboxed value type variable.

#if INEFFICIENT
      // When compiling the following line, v is boxed
      // three times, wasting time and memory
      Console.WriteLine("{0}, {1}, {2}", v, v, v);
#else
      // The lines below have the same result, execute
      // much faster, and use less memory
      Object o = v;

      // No boxing occurs to compile the following line.
      Console.WriteLine("{0}, {1}, {2}", o, o, o);