Loopt is strictly permissions based, and built to be secure from the ground up. You could, for example install it, along with a couple friends, to help locate each other at a concert or some big festival (this is really handy), and shut off broadcasting, or just ditch it later. It doesn't need to violate privacy; you have the ability to broadcast your location when you want to be found, and only to whom you want to be found by.
Do you not realise just how much fun it is to stand at one end of a stadium frantically waving for half an hour with your cellphone, trying to locate other people you know?
i can see how it would be useful, especially in work related sectors like taxi-services, hospitals etc. i would always dread if myself and my girl-friend had it that she would ask me why i had turned it off at such a time and grow suspicious...not that i am cheating on her or that i have a girlfriend...but its the sort of present that if i got it from one, i would break accidentally. great ap for parents and kids though. not great for cool kids.