Jo wrote some code (http://mappinghacks.com/openguides/) to do an SVG plot of where nodes with lat/long data are in relation to each other. I've modified it a bit to highlight stations to give an idea of scale, and here's the result:

http://london.openguides.org/nodemap/nodes_with_stations.svg

Stations are red, other nodes are blue. It's crude, but you can pick out several different Tube lines and see where the big clusters of nodes are.