It seems to be popular in Japan. I got on there and every that was added is Japanese or lives over there. My wife uses it to talk to her sister and her friends all the time. Nobody else I know has ever heard of it.
Yeah, it's the same in Korea. No one texts. It's all Kakao. That's the only time I ever used it, but it was good because I convinced my buddies back home to get it and we could text internationally for free. That being said, Android has hangouts now and I don't really know anyone who uses iOS, BB, or Windows, so I just use that with the few friends that care about data-based texting services.