One very cool feature in PHP 5.2 is the addition of an upload hook which makes a upload progress meter possible in pure PHP. Up until now, most upload progress meters required a PERL script to handle the upload.

ARTICLE - http://www.dinke.net/blog/2006/11/04/php-52-upload-progress-meter/en/
DOC - http://talks.php.net/show/torkey06/23
DEMO - http://progphp.com/progress.php

That does sound quite interesting, I'll have to look into it when i'm not so, half asleep