Seconds later, your recipient receives a link. If they are on a laptop or PC, they will see you on a Google Map -- it can be street or satellite view. Your icon will be moving in near real time, and your speed will be displayed. If you have selected a destination, it will show up on the map as well. It doesn't get easier than that.
If the other person has Glympse on their phone, they have the option to have the app's built-in map display your location. If you want to cut off a viewer before their allotted time is up, you can "expire" them. You can send your location to multiple people, which they can view simultaneously. I've used the app to let people know that I'll be late for a meeting or to display my position in traffic. You can also share your locations to Facebook or Twitter.
I have found Glympse to be reliable and quite helpful. You're in control of your location information, and can turn it off at any time, or let it run for the duration you specify. Of course leaving it on can have some battery implications, so be aware that sending hours of location information could leave your iPhone drained. Of course your location lags a bit behind real time. In my testing I saw 6-10 seconds lag for the person who was following my drive.
Glympse does not appear to send information when it is in the background when using iOS4, and that would be a nice feature. [Note: Some of our readers report it does work in the background, and I will take their word for it -- the developers say it does work, so my experience was obviously not typical. When I tested it people reported that my icon stopped moving.] There are other location sending apps around, but Glympse is easy and trouble free. Glympse is a universal app, and runs on the iPod touch and the iPad. iOS 3.0 or greater is required.