Well, at least the latest unique visitor (UV) and page view (PV) numbers released from Koreaclicks think so.
UV for Twitter measured in the last week of 2010 decreased by 6.3% from 3 months ago (Sept 2010) . This is more than 20% drop Page views for Twitter showed a more drastic decline of 44.2% measured in the same time period.
UV and PV for Facebook look promising, however. UV for Facebook showed a rapid growth of 72.3% in the last week of 2010 from 3 months ago. Page views grew by 42.6% in the same time period as well. (Stats from Koreaclick.com)
An article in Chosun speculates Twitter’s decline in popularity to be attributed to two factors: 1. Twitter users are said to be discouraged by one-way communication of public figures including celebrities and executives of large corporations. 2. Another is Twitter’s lack of interest and support in the domestic market, while Facebook is more active in communicating with Korean users and having Korean language support.
Facebook is now 12th most visited website in Korea according to Rankey, a company specializing in website indexing services. Twitter is ranked 24th.