Our friends at DebianPlanet have been lurking in the wiki and found this interesting piece by Joey Hess about secure apt.
Recently Debian's unstable and testing branches have begun to use strong crypto to validate downloaded packages. This is commonly called “secure apt” and was implemented in version 0.6. Since the documentation is fairly slim on how this all works from an administrator's point of view, this document will try to explain in detail how secure apt works and how to use it.
Read the wiki entry here
And here's where I spotted it at DebianPlanet.org