This is mightily impressive: more than 90 percent of South Koreans in their 20s, and more than one-third of the entire population of South Koreans, are registered users of Cyworld.
Cyworld is doing what Facebook is only trying to do: breaking even, and merging online shopping and social networking.
Part of the reason seems to be the market that Cyworld is dealing in. As opposed to majority of the rest of the world, Google does not have a major market share in South Korea. It is no coincidence that, as well, South Koreans generally do not prefer simplistic, pared down websites, like Google’s homepage. Instead content-rich, media-dense sites pique South Korean interest. Cyworld fits that bill.
PluGGd.in has a great analysis of the reasons for Cyworld’s success at their piece linked below.

The full story at PluGGd.in:
http://www.pluggd.in/technology/cyworld-unique-social-networking-revenue-model-3771/