Two small perl scripts (Intended for linux, may be adaptable to Windows) for working with books in EPUB format. May be useful.
I did create a utility, advepub, which losslessly shrank .epub files by disassembling them and applying jpegoptim and the advancecomp suite appropriately. This worked very well, but has now been superceeded by Minuimus, more versatile tool which can be used for the same purpose.
epubmeta.pl : Reads the metadata from an EPUB file. It can also extract just the document identifier, which is typically an ISBN number, but not always.