If twitter is the microblogging tool of the masses, identi.ca is the home of the geeks. An open source micro blogging solution identi.ca a little hard to use. Not as slick but more feature rich than twitter, users sign up and then... if your friends are not already on the site, you really have no reason to go to it. Unless you really like IRC chat rooms and updating builds of open source software, i would use twitter in place of identi.ca.