Trophaeum – I tested mod_deflate but I wasn’t happy with the results. I don’t think mod_deflate caches the gzipped content like mod_gzip does. When under load Apache served .html.gz files much faster than with mod_deflate gzipping .html files.
AFAIR, there was no mention of caching on the mod_deflate page. I can only presume that gzipping was done on-the-fly unfortunately.