It was about open source. DjVu was just an example. All that I know about it came from a quick google.
Which turned up [link|http://www.djvuzone.org/|http://www.djvuzone.org/] which advertises open source implementations. [link|http://djvulibre.djvuzone.org/|http://djvulibre.djvuzone.org/] has the standard implemented in GPLed format.
So yes. There is an open source implementation. I have no idea how good it is or isn't.
Cheers,
Ben