According to psychologist Dr Aric Sigman too much time spent on 'social' networking sites 'could alter the way genes work, upset immune responses, hormone levels, and the function of arteries, and influence mental performance.'
Seems obvious to me and I've never really understood the appeal of living one's life in virtual reality.
Article here: uk.news.yahoo.com/4/20090220/tuk-get-off-facebook-and-get-a-life-dba1618.html