The above <IfModule> block exists in httpd.conf outside of all the VirtualHost configuration. Do I need to specifically enable mod_gzip within each <VirtualHost> block?
Or would I be better off writing a PHP script that outputs my CSS and JS files, thereby getting compression via zlib and bypassing the need for mod_gzip entirely? I don't like this idea much, but I could do it if that's the best answer.
I finally made this work... problem #1 was that the directory in the mod_gzip_temp_dir directive didn't exist. It needs to exist, and be writeable by the apache process owner (nobody).