My guess is that most people aren't prepared to allow location tracking websites to have blanket coverage of their movements. Many services try to solve this issue by allowing the user to set the granularity of the location data being tracked. Fire Eagle, for example, allows the user to set the level of access to road, neighbourhood or city level.
Glympse however are betting on the fact that it isn't the degree of accuracy of location that concerns most people but the issue of time. Glympse therefore allows the user to share their location for a limited amount of time.
Using Glympse the user can use their smart phone to show their location on a Google Map for a specified period. To use the service you simply select a contact, set a duration, and hit send.
Here's the introductory video,