Interesting USA Today article here re multi-site churches. It claims that 'Of the USA's 100 largest churches, 67% now have two or more sites and 60% of the 100 fastest-growing churches also have multiple sites.'
Tim Keller serves 4 already in New York, with plans for 6 more in the next 10 years. He argues in their favour: "The core of the multisite concept is that a church must 'reverse the flow.' Instead of drawing people to the church, take the church into their world."