"Gwiboon" is like "Onew" in that it follows no pattern but at least it's close to the way it sounds. LOL I can hear a super American accent pronouncing "Guibun" as "Gue-bun."

Every time I see "Wheesung", it reminds me of Wee-Sing (http://en.wikipedia.org/wiki/Wee_Sing_Video_Series) because we had a bunch of those tapes when I was little. Wee Sing! Wee Sung!