Jeff Atwood tells me he’s thinking of leaving Twitter for Jaiku. Scoble wrote about how Leo Laporte already left. Strangely enough, I’m having a sense of deja vu. Twitter would do well to study the lessons learned in the history of Friendster vs MySpace. Building a Twitter clone is not rocket science. There is no huge barrier to entry. The only thing that keeps twitter on top of other services is their large user base. As danah boyd points out in this essay which compares Friendster vs MySpace, People use the social technologies that all their friends are using....