I doubt that the progress bar will stop the problem that sometimes on slow/large uploads, something will timeout and you'll be left with an unfinished upload. I don't know what initiates the timeout - if it's the server, or the browser, or the what. I also don't know what the workaround is - it may be a pref in the server itself or something you can't workaround in a CGI script

You might find this link helpful which discusses a common solution to this problem.