Korean, like Chinese, is written in syllabic blocks. While each letter of the Korean alphabet has a sound, they are combined together to form blocks like this: 한국 (Korea). However, there were attempts made in the early 20th century to break free of this. Thus 한국 would be written ㅎ ㅏ ㄴ ㄱ ㅜ ㄱ. It’s not exactly elegant and it never really caught on.
Over on the Pinyin news blog, they’ve discussed problems with converting Chinese words into Roman letters. Each Chinese character represents an individual syllable, not an individual sound. This is why you might see Toilets rendered as ToiLets.
You can sometimes see examples of this problem in Korea. Here are some entertaining attempts at Romanization at the Seoul Bus Terminal.