Beijing Subway vs. Tokyo Subway
I did a comparison of Beijing subway system and Tokyo Subway system.
As the capital of arguably the most fast-developing country, Beijing has been exerting all its effort in developing public transit system to cope with the challenges of increasing urban population. As of 2007, Beijing only had four subway lines in use; in 2015, however, Beijing is expected to own 28+ subway lines with 561 km in total network length (the longest in the world), where subway/LRT users will account for 23% of total travelers. (source: wiki-beijing-subway)
Here is Beijing's subway plan for 2015.
I visited Tokyo in 2005 for a students' cultural exchange conference, and I was really impressed by the service of the subway system there. Moreover, the subway system was not just a subway system; it was also an integrated area of shops, restaurants, malls, theaters, and other entertainment facilities.
By just looking at the topologies of the two systems, we can find that BJ subway is more grid-like, yet Tokyo subway network seems to have more junctions (I don't know if this fact can lead to shorter travel time, I guess it will).
Here is some demographic information. While Tokyo has about 12.8 million people, Beijing is home to 14.93 million (not considering immigrant workers from the inland area). The population density per km2 in Tokyo is about 5847, and in Beijing is 760. China still has a large rural area to be urbanized. Yet Japan has been trying its best to make full use of underground space due to its limited territory, which is a remarkable effort.