Gzip (or on Apache 2, Deflate) compression is a godsend. Rather than try to deal with changing content headers in code, with a few simple httpd.conf settings you can get nearly all the advantages instantly. Now possibly ancient browsers can choke on this, but it will work for everybody who has a browser built since the millenium – to accommodate the old folks we have a BrowserMatch condition. Add some simple expiration rules and you’ve probably sped up your serving by at least 70%.
Make sure you’ve enabled mod_deflate via LoadModule, then add this to the main section, or your virtual host(s).