우와 is definitely heard a lot, but to be honest I've not heard 자짠 much. Although it is more of a 학생-style word, and I don't usually hang out with 학생s. (forgive my mixing languages... ㅋㅋ) Students in Korea have a lot of slangish words that only they use. Like 헐 and stuff like that. Older people have their own way of speaking as well. The generation gap shows profoundly in their language, much more so than in English. Yeah, in English we have things like that too, but often it's only the younger generation doing something different, and the older generation often picks it up soon enough. Anyway, 우와 is super common. 자짠 is kind of a younger generation word, but if a white person of any age used it properly, it would almost definitely get a few laughs, and not in a bad way.

The two words are quite a lot used in spoken language.