I have told many people about the Dodgeball service (a service you and your friends can use to help each other meet up when you're out). Most of the people I tell about it have a positive initial reaction and express an intention to sign up for it. But when they actually visit the web site and start to sign up, they chicken out. Why?
I'm not sure what Dodgeball should do to make prospective members more comfortable. But somehow they need to do a better job of highlighting their strict privacy policies.