Dave Legeret silently fumed as the man seated beside him on the plane blasted techno music on his iPod at full volume. "It was kind of rude," recalled Legeret, 38, a jewelry designer from Sandy Hook, Conn., who was forced to listen while flying from New York City to Disney World in Florida with his wife and 8-year-old son. "Listen to it at a level that just you can hear it, and everyone else doesn't have to be subject to it." Apple Inc.'s ubiquitous iPod is best-known as an instrument of solitude - unless the user ignores standards of etiquette...