I was advised by our corporate travel consultants that I should get a visa. Given the current international climate -- there was an article in last Thursday's Wall Street Journal about how other countries are retaliating for the current U.S. fingerprinting and visa application requirements -- this may be a prudent course of action.
The Korean embassy page that is linked to from the IETF meetings page (<http://www.koreaembassy.org/visiting/eng_visas.cfm>) makes it pretty darn clear that US folks should get a visa. They do have a link from that page saying how wonderful US-Korea relations are, of course.
Showing up in the airport without a visa and saying "but someone at one of your consulates told me I didn't need one" may go over as well in other countries as it does in the US...
--Paul Hoffman, Director --Internet Mail Consortium