I use it a lot with my wife:
1) She doesn't always leave work at the same time. I can check and see where she is so I can know when to start making dinner without having to bother her with constant phone calls. "Have you left yet? Have you left yet? Where are you now?"
2) Inversely, when I DO need to call her and I know she's driving somewhere I check to see if she's arrived before I call. There's no reason to add to the number of people talking and driving out there. I'm happy to wait a few more minutes.
3) I've used it a lot when the plan is "meet me at the subway station" or "I'll be in the grocery store parking lot." It sure beats the previous method of "Where are you? What? Your left or my left? Do you see me waving? No, that's some other guy with the same coat as mine. I see him too, walk towards that spot."
Real-world example: Many of the subway stations here have 2 'pick-up' lots. Usually in totally opposite directions. When I called to ask if she's in the north or south lot I'd usually get "Uhmmm...there are busses by me?" I don't have to have that conversation anymore.
4) I haven't been to a theme park yet, but I imagine it'll be super-useful at Disney World this year. We'll often split up for an hour or two, and it's hard to get someone on the phone when you're out in a noisy theme park and it's hard to hear your phone ringing.
