Trap Enter (or any other key).

This is in the same line of thinking as the Hook F5 mention.

Sometimes it is usefull to "trap" a key - especially enter - and to do something other then the normal form submit or what ever.

function trapEnter(e)
{
  var keycode;
  if (window.event) keycode = window.event.keyCode;
  else if (e) keycode = e.which;
  else return true
  if (keycode == 13)
  { 

    //If enter should do nothing
    /*
    e.returnValue = false;
    e.cancel = true;
    return false;
    */
    //Otherwise - do stuff
  }
  return true;
}