Low tweeting is a big issue, since it negates some of the Twitter narrative. The whole "pulse of the planet" realtime search thing isn't really valuable if most of the users aren't contributing to the corpus.
Also, if it's just a handful of the users creating the value, then the switching costs are much lower. You'll go to "where the celebrities are" (which may turn out to be Facebook, or something else) and not the harder to move "where are your friends are".
Also, if it's just a handful of the users creating the value, then the switching costs are much lower. You'll go to "where the celebrities are" (which may turn out to be Facebook, or something else) and not the harder to move "where are your friends are".