A number of years back I was very excited about DJVU and used it to compress my scanned documents. But at a certain point did I realize that scanned bitmaps (as well as TeX'd documents width pk fonts) in PDF were just as small, and I stopped using it, as PDF is much more widely available. I'm not sure if the almost equal sizes of djvu and postscript were because bad djvu compressor or because the PDF compressors improved at some point. I would be interested to hear if someone else has other experience.
Regards,
Dov