I talked to Frederic Lardinois on Friday and he posted a writeup about echoecho today.
“One problem that has hindered the widespread adoption of location-based services in the past is the fact that sharing location data with random people is something that a lot of people feel rather uneasy about. Echoecho routes around this problem by using a very nifty permission-based solution. Whenever you request somebody’s location, your friend has the option to completely ignore your request. At the same time, if somebody responds to your request, that person will also be able to see your own location. This should help to alleviate some of the social issues that are often associated with location-based social networks.”