The most effective way to tally up the stupid part of the world's population since the lottery. Also facilitates studies of their behavioral and herding patterns (i.e. following a person on tweeter). A perfect tool for stalkers and burglars since twitter users voluntarily disclose information about their whereabouts and activities.
"Hey I found this huge group of people on twitter who twit about every mundane detail of their boring lives. I think I'm going to follow them."