Second Life is a fantastic example of how not to develop a community. The creators put too much thought into persuading people to join the community and too little in keeping them.
They spent money on marketing, advertising, PR and not a penny on community management. Nobody was helping build boundaries, develop groups, highlight the common purpose, document and spread the shared experiences.
Once the novelty and the PR died, Second Life died. Nearly. What now survives in Second Life is a the same tiny Second Life community that existed before the PR wave.This community isn't about the novelty of virtual worlds, it's about the other people that enjoy the game.
Second Life is an easy target. There are lots of communities that fail to think their community through.