"The evangelists of social media don’t understand this distinction; they seem to believe that a Facebook friend is the same as a real friend and that signing up for a donor registry in Silicon Valley today is activism in the same sense as sitting at a segregated lunch counter in Greensboro in 1960. “Social networks are particularly effective at increasing motivation,” Aaker and Smith write. But that’s not true. Social networks are effective at increasing participation—by lessening the level of motivation that participation requires."
So Twitter and Facebook are good for getting people to vote for your band on that online competition, but quite rubbish when you need someone to help you move house. As ever Gladwell's stating the obvious here ( in an interesting way, no doubt), but there's enough people who think a tweet will move mountains for the message to be necessary. link