Then there's Google's Latitude, which works on the G1 just fine. The iPhone too except you have to use Safari since there is no standalone Latitude app for the iPhone. See, Apple rejected it.
But I wonder how many folks actually use these geo locators. To put it in a better term, friend locator. I have yet to find a compelling reason to use such services. Tagging pictures and video. I'm okay with that. However, I don't see the need to broadcast to everyone where I am every single moment of my life.
I can see one possible scenario where I might contemplate using Latitude. That's if I go on vacation and I want to folks at home to know where I'm visiting. This allows them to zoom in on my location and, if there is Street View available, they can get a sense of where I am and what I'm seeing around me.
Even so, locations can be spoofed. I've done it while testing Latitude out.
If you use Latitude, Loopt, or any other services, let me know how you like it and how you're using it.