150 followers is the magic number. In a particularly
interesting data point from the survey, Sysomos found that Twitter
users tended to "follow back" all their followers up until about 150
connections. Then the reciprocation rate fell off dramatically, which
seems to indicate that this number may be the crossover point where
people shift from using Twitter for more personal use to using it more
for "lifecasting" their thoughts and actions to a community of people
who they feel varying levels of connection to.