Automatically set the TimeZone in Rails >= 2.1

application.js

// detect time zone
Event.observe(window, 'load', function() {
  var date = new Date();
  date.setTime(date.getTime() + (1000*24*60*60*1000));
  var expires = "; expires=" + date.toGMTString();
  var offset = -(new Date().getTimezoneOffset() / 60);
  document.cookie = "timezone=" + offset + expires + "; path=/";
});

application_controller.rb

class ApplicationController < ActionController::Base
  before_filter :set_timezone
protected
  def set_timezone
    tz_off = cookies[:timezone]
    Time.zone = ActiveSupport::TimeZone[tz_off.to_i] unless tz_off.nil?
  end
end