I’ve known for quite a while that SMIGRATE backups (FPB)s were simply renamed CAB files.  Today I had a collegue show me that STP files are just renamed cab files too.  When you create a template — either for a list or a site the resulting STP file is just a renamed cab file with a manifest.xml file.  I’m not sure what I’m going to do with this new found knowlege but it is definitely cool.  (It might make it possible to apply a template to a different site definition for instance.)