On testing, development, and some other server and workstation environments, I use a variety of package repositories (with CentOS, for example, these include: remi, epel, rpmforge, jpackage, and others).
For various reasons, I maintain several versions of CentOS, Ubuntu, etc - and being able to draw from any of those repositories is handy.
However, the overhead of managing which ones are available where is a huge pain once you exceed a couple machines.
Would it be worth the energy, space, and time to maintain a full mirror of those repos into a central, localised point where my systems can all go look? If not, what other viable option(s) are there?