When I was stationed in Japan, I took a week and went over to S. Korea. All I can say is its a neat place to visit and experience the food. Also, I spent ALOT of money on buying items, it reminds me of going to mexico with everything available for barter, including new suits (i got a few of those 3-piece custom made and a cashmire overcoat for about $200).
I am one that likes to get out of the normal tourist cities and go see the countryside, most everyone will try to work with you when ordering food and drink. Also, keep your ID handy as their is alot of checkpoints to go through if you leave Seoul.
I would recommend the DMZ tour and the tours of the underground tunnels N. Korea built to infiltrate. Its pretty awesome, sobering sight to go by the airport and see the Patriot missiles pointed North for protection.
You'll have fun just wondering around and getting lost. There is a curfew set for all Americans to be in by a certain time (can't remember if its 12am or 2am).
