WinForms.rb

require 'System.CoreEx, Version=1.0.2521.104, Culture=neutral, PublicKeyToken=31bf3856ad364e35'
require 'System.Interactive, Version=1.0.2521.104, Culture=neutral, PublicKeyToken=31bf3856ad364e35'
require 'System.Reactive, Version=1.0.2521.104, Culture=neutral, PublicKeyToken=31bf3856ad364e35'
require 'System.Windows.Forms'

include System
include System::Collections::Generic
include System::Linq
include System::Windows::Forms

class TestForm < Form
  def initialize()
    self.Text = 'Hello IronRuby'
  end
end

form = TestForm.new

clickObservable = Observable.method(:from_event).of(EventArgs).call(form, 'Click')
clickObserver = Observer.method(:create).of(IEvent[EventArgs]).call(
  lambda {|on_next| MessageBox::show('clicked') },
  lambda { |err| puts err.to_s },
  lambda { puts 'completed' })

clickSubcription = clickObservable.subscribe(clickObserver)

Application.run(form)

With IronRuby 1.1, it looks like you could do something like

using_clr_extensions System::Linq
using_clr_extensions System::Observable

# Snipped form and includes ...
clickObservable = form.from_event('Click')
clickSubscription = clickObservable.subscribe(
  lambda { |on_next| MessageBox::show('clicked') },
  lambda { |err| puts err.to_s },
  lambda { puts 'completed' })

Application.run(form)

I haven't tried this, but it seems plausible.

Well nevermind! Looks like you've already done it! :) Cheers!