It’s sometimes helpful to keep your machines using a list of apt archives to use, rather then a single mirror, because redundancy is good. Rather then using (the great) services like http.debian.net or ftp.us.debian.org, you can set your own mirror lists using apt’s mirror:// protocol. All of this is ultra unstable, so be a bit careful when using this. I’ve been using mirror:// for a few months now, and it seems fine (even have my servers using it), but it was a bit of a pain to set up....
