Official PlayStation 3 firmware update files basically are uncompressed archives containing different subparts.
pupextract program I wrote basically is a one-hour project which just takes a firmware update file as input, and separate the different subparts into different files. One of these output files, which I called update.tar, is a simple GNU tar archive, containing the (encrypted) files for the firmware update. Another one contains the end-user licence agreement (EULA), while some contain basic information such as the release version number, and others contain empty or unknown data.
Not sure it will be useful for many people, but I decided to release it under the GPLv3 free software licence.