Ning is one of the best Web concepts I have seen since I began using the Internet in the late '90s. The others being: Email, search engines (www.clusty.com, www.technorati.com www.a9.com,), maps (www.maps.google.com, www.maps.yahoo.com/beta and www.mapquest.com). The others that come close to Ning are www.del.icio.us and www.digg.com.