Well, LinkedIn already has the professional identity market locked down, so an entrant would probably want to focus on personal/private identity. One approach

Well, LinkedIn already has the professional identity market locked down, so an entrant would probably want to focus on personal/private identity. One approach would be something targeted at dating and meeting people who share your preferred activities, while letting you manage how much of your real identity you want to reveal. Think Second Life meets FourSquare, with avatars, pseudonyms and various exaggerated expressions of individuality. Another approach would be something for sharing information privately with a group of existing friends, building group identity. Think private clubhouse.