I had to give up on progress bar because I could not find a way to get it to automatically start issuing ajax requests on page load. I have a page that starts a process and another page that displays the process and I wanted to use progress bar to graphically show progress. I ended up using poll and a text representation of progress because poll has an autoStart capability.
It would be nice to have the ability to auto start the progress bar while in ajax mode.
It also would have been nice to know you HAVE to start the progress bar component when in ajax mode.