EDIT: Please see this post on the stack exchange for updated instructions on how to use this.

For Lucid this is how you will set up a caching apt server for machines inside your network.

On the server:

sudo apt-get install squid-deb-proxy avahi-utils

Avahi will now advertise that there is a caching proxy available on your network! Now to tell the rest of your computers to look for it. On the client:

sudo apt-get install squid-deb-proxy-client

You might want to set this up as the demand on the package servers increases over the next 2 months. This is also great for laptops because if a caching proxy is there it will use it, if there isn’t one it won’t care. Thanks Michael Vogt!