1. uniq_bench.rb

require 'benchmark'
require 'set'

source = 100000.times.map { rand(100) }

n = 100
Benchmark.bm(5) do |x|
  x.report('uniq')  do n.times { source.uniq  } end
  x.report('uniq!') do n.times { source.uniq! } end
  x.report('set')   do n.times { Set.new(source) } end
  x.report('hash')  do n.times { source.each_with_object(Hash.new) {|i, h| h[i] }.keys } end
end

2. ruby 1.9.3p125

ruby 1.9.3p125 (2012-02-16 revision 34643) [x86_64-darwin11.3.0]
            user     system      total        real
uniq    0.770000   0.000000   0.770000 (  0.777292)
uniq!   0.010000   0.000000   0.010000 (  0.011109)
set     0.010000   0.000000   0.010000 (  0.003713)
hash    0.000000   0.000000   0.000000 (  0.001277)

3. jruby 1.6.7

jruby 1.6.7 (ruby-1.9.2-p312) (2012-02-22 3e82bc8) (Java HotSpot(TM) 64-Bit Server VM 1.6.0_31) [darwin-x86_64-java]
           user     system      total        real
uniq   0.555000   0.000000   0.555000 (  0.555000)
uniq!  0.015000   0.000000   0.015000 (  0.015000)
set    0.208000   0.000000   0.208000 (  0.208000)
hash   0.089000   0.000000   0.089000 (  0.090000)