I've had 3 days experience with the Tokyo Metro subway system. It's huge. and seems incredibly efficient. Most of the stations are underground and it's like mini-cities for some Metro stops. Each station has shops -- at least a small grocery/AM-PM type of store and maybe a coffee shop.
Tonight I got to experience rush hour in one of the busiest Metro stations in Tokyo (and I've heard the world). Shinjuku Station. I'm not sure how many train lines run through this station but it's got to be at least 10 lines.
I turned to head up the stairs to the platform and just saw mobs of people streaming down the stairs to change trains or exit. I dove for the edge of the stairs to not get trampled and muttered
"Oh Shi@#!" to myself! Then I slowly worked my way up the side of the stairs against traffic. I really felt like a salmon swimming upstream. Wow -- that was an experience.
(update 11/26)
Riding the Hiroo subway line (non-commuter hours!):