There are several different types of clothing/accessories shopping in Seoul:
(1) High-end department stores (of which there is no shortage); look for familiar brands like Louis Vuitton, Fendi, and Marni, as well as some newer Asian designers.
(2) Malls. Shopping in malls is a totally different experience in S. Korea, and one that didn't really appeal to me. It's sort of like walking into a beehive but with disco lighting and loud music.
(3) Underground arcades. These are located at the subway stations; made up of different booths of clothes, shoes, jewelry, etc.
What I learned:
(1) If you live in the States, do not buy luxury goods in Seoul. Even tax free, the prices were outrageous. The Chanel Jumbo Classic bag that I've been lusting over: in the states, $2700.00; in Seoul, $3400.00. This price difference was true in pretty much all of the boutiques. A LV Azur Speedy: here, ~$700.00; there, $815.00.
(2) The Cyndi Tote by Chloe is more gorgeous in person than I'd imagined, but totally impractical - empty it weighs a good 10 pounds.
(3) Malls in Seoul make me physically ill -- dizzieness and nausea included.
(4) A lot of places don't have fitting rooms, so you definitely have to learn to eyeball what's going to work on you and what isn't.
(5) Girls there dress impeccably. Not once did I see someone in sweats that had something spelled out on the behind. Dress code: ruffly blouses over tasteful mini skirts, shift dresses, floucy skirts with cap sleeve blouses, expensive bags.
(6) And last but not least, jewelry, jewelry, jewelry. At some of the smaller antique stores and embroidery shops, I really had to reign myself in - I love oversized rings and there were some truly beatiful pieces. The rings made use of Amethyst (the national stone), Jade, and Amber. Most were set in silver, with lots of intricate detail and carvings. In the end I settled on this one -- it was so unusual and I couldn't stop thinking about it!