> The difference increases in real world reports.

This and some other tips seem specific to either ruby 1.8 or 1.9.
While StringIO seems much faster with 1.9, in my world, the difference
is rather marginal with 1.8. Also, the following is slightly faster
with 1.8:

times = ARGV[0].to_i
times.times { STDOUT.puts "hola mundo" }

YMMV etc.