If you're like me, you've got a few computers sharing a home network. Mine happen to bo all Ubuntu, so we've got a lot of redundant downloading of updates going on. I've typically used apt-proxy to solve this problem, but it's not as straightforward to set up as it should be and all the clients need to have their proxies modified. Not a PITA, but much more difficult than Apt-ZeroConf.
As the name implies and the sparse web page illuminates, Apt-Zeroconf uses auto-discovery of other similarly-configured clients on your network and pulls packages from their package cache instead of downloading from a mirror, saving you a lot of bandwidth. It's only at 0.41 now, but it appears to wok well in my limited testing of it.
Visit the web page to install it. You can download the .deb or add the reposiory to your list if you want to stay current. There are no screenshots and no need for any configuration on your part. Just install and it should be working in the background and ready to go.
Thanks to a comment on Ubuntu Brainstorm for pointing me to this package!