var fn = Cufon.registerFont;
Cufon.registerFont = function(data) {
    fn(data);
    some callback...
}

Cufon (http://cufon.shoqolate.com) font  files automatically invoke Cufon.registerFont method after load. Since we cannot change files format, we should override this method so it will call our custom callback. This is useful if we want to add some custom functionality which will run after Cufon font is loaded.

Quick callback for Cufon.registerFont

JavaScript