Groucho Marx would not join any club that would have him as a member. By the same token, I always knew Facebook would become uncool the moment I joined. And lo, it has come to pass. According to Nielsen Online, the social network has suffered its first decline in the UK: the number of users fell from 8.9m in December to 8.5m last month.

Facebook was not originally for people like me, but for students. It started at Harvard and expanded via other elite universities. Facebook's explosive growth began when it opened up to everyone. Once your parents join, it becomes a less interesting place to hang out.