Using apt-cacher-ng here on Squeeze, tried the others and found that the most reliable. Like the alternatives (apt-move, approx..., ) caches what you download during apt-get/aptitude operation to a "repo-image" format. Is very much self-maintaining once set up and works well as an apt server.on LAN
Certainly earned it's keep here while main mirrors were down recently
To mirror the whole lot... it's rather large!
David