Spent quite a bit of time in Seoul and Osan (while in the Navy), years ago.
I found Korea in some ways to be like a low-rent version of Japan (if you have been to Japan), and I found that the locals are more likely to take advantage of tourists in Korea (especially in the bar/redlight districts), so be aware of your surroundings and be careful.
Korea is notorious for black market bargains, with counterfeit anything you can imagine.
South Korea has been going through rapid social transitions since the 60's. Since that time, Christianity has surpassed Buddhism as the major religion, although there are numerous cult-like Christian sects in Korea too (think Rev. Moon, and even stranger variations).
Another thing to keep in mind, is that the Korean people have been living under the shadow of war ever since fighting in the Korean War stopped in the 50's. I remember during one visit, we were driving down a freeway, when police lights and sirens suddenly popped up alongside the road, and everyone started pulling over so that some military jets could do a practice emergency landing on the freeway (I guess in case the airport was bombed). A very surreal peacetime experience, to see a jet speeding past you on the freeway (wish I had a camera with me for that one).
Have a nice trip!
ADG