The importance of online social spaces is growing. New Web 2.0 resources allow the creation of social networks by any netizen with minimal technical skills. These communities can be extremely narrowly focussed. In this paper, I identify two potential costs of membership in narrowly focussed virtual communities. First, that narrowly focussed communities can polarise attitudes and prejudices leading to increased social cleavage and division. Second, that they can lead sick individuals to revel in their illness, deliberately indulging in their disease (...) and denying the edicts of the medical profession. I specifically examine illness communities centred on the now defunct Multiple Personality Disorder. I highlight these potential problems and point to some technologies that may help combat them. (shrink)