I tried running apt-cacher but I can't get it to work at all. Whenever I try to update another machine, it stalls and apt-cacher requires a restart. I am now trying out some new tips from this page:
ubuntu-tutorials.com/save-bandwidth-during-updates-with-apt-cacher-ubuntu-610/
Especially this one:
Acquire::http::Proxy "http://apt-cache-machine:3142";
in the apt conf file.
UPDATE November 20, 2007: I'm no longer using apt-cacher. Instead I'm using squid or caching apache web server proxy, depending on the setup.