Herding Firesheep in New York City: He sat down in a Starbucks, opened up his laptop and started gathering profiles, then sent messages to people whose facebook accounts he could access warning them of the security flaws. Some people closed up and left, but some just ignored his message and went on with their day. Confused, he sent another message, but they just didn't seem to care and continued using their accounts.
He was appalled that people, even when warned, would ignore a security flaw, but it's actually well known that people reject advice. The interesting part of the story comes with Cormac Herley's paper "So Long, And No Thanks for the Externalities: The Rational Rejection of Security Advice by Users" -- it turns out that it makes perfect sense that people refuse to do security things, and fixing the flaws that firesheep draws attention to is just another example of where security advice just isn't worth following.
You can read the full version of this post on Web Insecurity: Apathy or sensible risk evaluation: why don't people care about security?