How it works:
A person you request location from receives an SMS message which is interpreted by the app. In case person doesn't have app installed they may click on a link in the SMS message to find out what did they just receive from you.
When app is on their phone they get a notification and can approve your location request by specifying whether it should be provided by network or GPS provider. As soon as approximate location is determined it is being sent back to you as SMS message.
Then you receive a notification which in turn opens Google Maps to display their location. Simple!
You can let people look up your location anytime but given that you always receive SMS messages in your messenger inbox there is no way people can stalk you without you noticing it.
Also given that it goes through SMS directly two things are in place:
Some charges depending on your phone carrier may apply;
Your location information is not shared with any 3rd party server;
Plans for future:
Implement a phone number confirmation and send requests/responses through SMS only if other person doesn't have app installed, otherwise communicate through internet (Google Cloud Messaging);
Could make it look more nicely; :-)