I'm another Stanza fan, yep. Open the book. File > Export Book as > ePub (or whatever) and save it. Once in a while I'll hit font encoding problems but 99% of the time its painless.
I find it much faster and easier than Calibre. I also find Calibre limited in its functionality vs. my needs (Mac, books on a RAIDed NAS, large and varied collection I want to organize/search/sort through) -- its easier just to use folders and deal with the books individually. I had such hope for Calibre from all the praise it gets
.