It has been raining all weekend, but even in the absence of rain, I have found that long distance buses usually arrive late in South Korea. I just got back on a five and a half hour bus ride. The high speed train takes about an hour and a half to cover the same distance, and normal trains a little over 3 hours.
While buses do get a special lane (the blue lane) on South Korean highways, they are not separated from other traffic. Sometimes other traffic comes into the lane, and sometimes a bus trying to get across the other stopped traffic lanes ends up blocking the bus traffic in the dedicated lane.
A lot of people have recommended I take long distance buses to get around South Korea over the upcoming Chuseok holiday (Korean Thanksgiving), but I think it will be better to stay within the confines of the Seoul subway/rail system. It is quite extensive and covers several nearby mountains. Besides, it will be cheaper, good for me while I pay off my debts accumulated over the summer.