Well, there is another option for PHP but it relies on perl code for low level issues. Take a look at
raditha.com/php/progress.php/
Works for me at client's site and I had no problems of using this Megaupload though it's not pure PHP (client has Linux, khm, LAMP). Sorry I don't have time to compare it with PHProgress Bar since I wasn't aware of this class before last PHPC newsletter but - this is the forum, so somebody will probably publish comparison.