It is Little Seoul, mostly in Annandale, spilling over into West Alexandria. The number of innovative Korean restaurants continues to increase and they are usually crowded. I love the new place devoted to the many forms of Korean porridge. Seoul Gool Dae Gee Honey Pig on Columbia Pike has the best decor (and the pork neck) around. TodamSoonDooBoo (also known as Tofu House, next to the Giant, straddling 236 and Columbia Pike) has dumpling soup and tofu. The two branches of Shilla Bakery and Le Matin de Paris give Virginia a cafe scene. Much of my eating out is now Korean or in the new Vietnamese places in the Western Saigon interior branch of the Eden Center; either that or Ray's Hell-Burger, Hong Kong Palace, Thai X-ing, or the now-reopened Nava Thai, right next door to the shuttered old branch.
Annandale used to be a nice appendage to the peak places to eat. Now it's the epicenter, the main culinary show, and also the coolest place to hang out.
Addendum: Here is a good article, which mentions Korean food as the next trend to come. Let's hope not.