Gnucleus does indeed do a mapping, but it's really just an instantaneous snapshot of the current "horizon" at the moment you hit the button.

The Python language program - the name escapes me - shows the network in realtime... fascinating to watch, actually. It doesn't actually do any file sharing itself, it just displays the connections as they grow, interconnect, and log off.

It takes a bit of horsepower to render the graphs, though, and could be better used for system applications. I'm just waiting for a OpenGL or Direct3D screensaver to render the horizon in glorious 3d.