Facebook drops in the UK

The Guardian is reporting that in the UK Facebook has posted it's first loss of users (article), down 5% from December 2007 to January 2008. While certainly not a sign of the end of days for online social networking, it will be interesting to see what Facebook's response will be. Why were the nearly 400,000 members lost? MySpace and Bebo also posted user losses, but Facebook was hot on a 17 month spree gaining 712% in the previous 12 months. Could a push from more specific networking sites undermine the dominance that Facebook currently enjoys?