Citation: http://www.straitstimes.com/breaking-news/asia/story/taiwan-tells-its-citizens-delay-trips-south-korea-20130411
I think it must be dangerous to visit bordering areas such as Kaesong industrial area, which is the only North Korean territory South Korean citizens are allowed to visit.
But, I don't think it's dangerous to visit Busan or the other southern parts of South Korea.
What is needed for travellers is to learn the detail information of their spots.