Do I need all the default apt mirrors to be active?

Knoppix 3.7 has a lot of mirrors active by default. I use Synaptic, and the list of repositories (which I assume is the same as /etc/apt/sources) is around 100 when I do a reload. I've disabled a handful of them and added main contrib and non-free for stable, testing and unstable from a mirror in Australia. However, the package lists take a while to download each time, as it checks around 100 different repositories/directories. As well as the main stable, testing and unstable trees, there's security, non-us, experimental and a heap of others. Have most people left these active? What should I do?