class Thingy
  is_eventable
end

@thingy = Thingy.new
@thingy.event = 'created'
@thingy.actioner = @user
@thingy.save!
# Event created with polymorphic link to @thingy and @user

# some time later
@thingy.update_attributes! params[:thingy].merge(:event => 'updated', :actioner => @user)
# Event created with polymorphic link to @thingy and @user

# even more time later
@thingy.wotsit = 'parp'
@thingy.no_logging = true
@thingy.save!
# No event created