I am currently in Seoul vacationing and this app has been indispensable. I figured out the subway routes from Incheon airport to my hotel in the Dongdaemun area and plotted out and saved all the routes to my tourist destinations for the upcoming week. I can quickly refer to any routes because the data is saved locally and I can plot routes on the fly with the simple and effective interface. No data connection is needed ( I have a US based iPhone with no cell service in Korea).
With additional updates (mainly having a built in search box at the main map screen) this app will only get better.
A big kudos and thank you to the developers or this wonderful app. My travels have been so much easier because of it. This is the BEST metro app for Seoul, it is money well spent.
mj-monk about Seoul City Metro - Seoul, South Korean Subway Guide