I've had it with apt-cacher
I thought apt-cacher was an improvement on apt-proxy. Boy was I wrong. It's been giving me a lot of headaches. Whereas apt-proxy needed the odd restart, apt-cacher needs files to be deleted from it's cache every now and then...
What a pain.
Now I've switched back to apt-proxy, and with a bit of squid tweaking (so that local network traffic isn't cached, or passed to the SAIX proxy) everything is working well again.