Since the groundbreaking studies by Stanley Milgram[1], human society is known to be a small-world network. Milgram found that any two people in the world, chosen at random, are connected to one another by typically six intermediate acquaintances. Social networks of such topology allow for the rapid spreading of news, rumours, jokes or fashions. Diseases, transmitted from person to person, can result in global epidemics. Small-world networks are the focus of recent interest because of their potential as models for the interaction in complex systems. There are different classes of small-world networks[2], but they all have in common that besides high local connectivity there are also some long-range connections. Only recently, many different systems have found to be small-worlds, the World Wide Web[3], food webs, protein networks[4], iHOP, the scientific community...