Active adult communities represent only a tiny fraction of the total housing landscape, but their popularity is on the rise. The number of 55-plus households choosing to live in age-qualified communities grew from 2% in 2003 to 3% in 2007, according to Census data. And that number will likely continue to trend upwards as baby boomers--the second-largest generation in U.S. history after their echo-boomer children--begin entering their retirement years. But winning over mature buyers often means thinking outside the house and creating irresistibly amenity-rich environments, as you'll see in this slideshow.