As the thread poelinca provided suggests, there are some nice plugins available for this functionality.
If you don’t like the plugin idea, another simple solution would be to simply trigger a “resize” event on the div whenever the content is modified. Then you could monitor it with resize() as expected, utilizing an elegant observer pattern.
function appendContent($div, content) {
$div.append(content).trigger($.Event('resize'));
}
$div.bind('resize', function(e) {
// all your magic resize mojo goes here
});