Source Recently, I wrote about a study written by virtual worlds consultancy kzero.co.uk, which reported that membership of virtual worlds grew by 39% in the second quarter of 2009 to an estimated 579 million. Today, I received an update from the Linden Lab and it appears that Second Life is experiencing a second life of its own. This story begins with an impressive milestone: Second Life Residents have transacted the equivalent of more than $1 billion  with each other while…