gistfile1

<form ...>
  <input type="checkbox" name="user[email_enabled]">
  <input type="radio" name="user[email_settings]" value="pm_daily">
  <input type="radio" name="user[email_settings]" value="pm_instant">
  ...
</form>


class Controller
  def update
    @user = User.find(params[:id])
    @user.update_attributes(params[:user].except(:email_enabled, :email_settings))
    update_email_settings(@user, params[:user])
    @user.save!
  end

  private

  def update_email_settings(user, params)
    if params[:email_enabled]
      if params[:email_settings] == "pm_daily"
        user.enable_daily_emails
      elsif params[:email_settings] == "pm_instant"
        user.enable_instance_emails
      end
    else
      user.disable_emails
    end
  end
end

class User
  
  def enable_daily_emails
    self.pm_daily = true
    self.pm_instance = false
  end
  
  def enable_instant_emails
    self.pm_daily = false
    self.pm_instant = true
  end
  
  def disable_emails
    self.pm_daily = false
    self.pm_instant = false
  end
end