Apt-proxy is no longer available in Debian 6.0, so finding a successor has become a mandatory task when upgrading my home server today.
I chose apt-cacher-ng after some research on the web. Looks like a promizing quality project, and migration was quite easy with the help of a complete "Howto replace APT-Proxy with APT-cacher-ng" . And I learned, that now I have an APT proxy for the first time, while apt-proxy wasn't a real one - just by it's (misleading) name.
After a short and smoth setup and data migration again I'm glad to have been pushed one step ahead. This is the Debian way, not exactly easy and compfortable at all times, but certainly worth the hassle. Debian devs, thank you!