If you price your product on the assumption that the average customer only uses 5% of their bandwidth then it doesn't take many customers using 50% or 100% of it to really spoil your economics
Personal Telco has some interesting opinions on this: http://www.personaltelco.net/index.cgi/StealingBandwidth?action=highlight&va lue=CategoryPhilosophy (quoting) "Traditional broadband providers cry foul when users take their cable modem or DSL connections and beam them to friends, family and passsers-by through Wi-Fi networks. "It constitutes a theft of service per our user agreement," says AT&T Broadband's Sarah Eder. But at least one very important observer doesn't buy that. "I don't think it's stealing by any definition of law at the moment," says FCC chairman Michael Powell. "The truth is, it's an unintended use." apl