We're looking for a solution to keep thousands of html/image assets inside a .zip archive, and decompressing single files on-demand as a local web server needs access? More than a couple hundred files or so on the iPhone OS file system absolute kills the backup process, and is probably not advisable for the flash disk either.
Solutions we've looked at are of course zlib and the unzLocateFile and the nice Java classes ZipEntry (would be nice to have in C…).
unzLocateFile doesn't seem to take a relative path, which makes duplicate filenames inside different dirs complicated.