GUI state update using callbacks?

One of the aspects GUI development is setting the enabling/disabling
of widgets. This can be tricky and also burdensome to program. Today I
came up with the idea of using a callback system. It think it's an
interesting concept and I would like to know your opinions about it.
Following code will explain more:

typedef boost::function< bool() > Condition;

class Widget
{
public:

  void setEnabled(bool inEnabled)
  {
    ::EnableWindow(mHandle, inEnabled);
  }

  bool isEnabled() const
  {
    return TRUE == ::IsWindowEnabled(mHandle);
  }

  void setEnabledCondition(Condition inCondition)
  {
    mEnabledCondition = inCondition;
    startTimer(boost::bind(&Widget::timerEvent, this, _1, 10); // call
setEnabled every 10 ms
  }

  void timerEvent(TimerID inTimerID)
  {
    bool enabled = mEnabledCondition();
    setEnabled(Enabled);
  }

private:
  HWND mHandle;
  Condition mEnabledCondition;
  Condition mVisibleCondition;
    // etc..

};

Data * data = new Data;
Widget * submitDataButton = new Widget;
submitDataButton.setEnabled(boost::bind(&Data::isValid, data));

I think this would be very useful. It can be used for others methods
like "setText", "setVisible", etc..
The only thing that worries me is the idea of using a timer. I worry
that it would cause performance problems, especially since there would
be a timer for each widget. However, this could be solved by using a
global timer.

However, I suspect that there might be simpler solutions that I am not
seeing right now.

Any thoughts, or ideas?

--
      [ See http://www.gotw.ca/resources/clcm.htm for info about ]
      [ comp.lang.c++.moderated. First time posters: Do this! ]