Don't get me wrong, I'm all in favor of privacy. But there are times and places when you very much want certain other people to know exactly where you are, without you having to do anything.
The release of Find My iPhone with iPhone OS 3.0 came at a perfect time for us, since Tonya got an iPhone at the start of the summer, just as she was beginning to train seriously for the 100-mile, an annual fundraising event around here. As the summer progressed, Tonya needed to do ever longer training rides that would take 3 to 7 hours and cover 30 to 75 miles. (For the record, on 12-Sep-09, she did the full 100 miles - an amazing achievement!)
During those rides, she always had her iPhone in her seat pack, turned on, but not attempting to run any special apps. When she stopped to drink or have a bite to eat, she would sometimes use Twitter to send me direct messages that would pop up on my iPhone courtesy of Boxcar, just so I knew she hadn't suffered a breakdown, injury, or accident.
But she didn't stop often, and it wasn't always convenient for her to pull the iPhone out, particularly if it was raining. So although I didn't worry much, there were a few times when she was quite late in returning home because she'd decided to ride further than expected, or she stopped longer than she thought she would.
On those occasions, and every so often during those long weekend rides, I'd log into her MobileMe account and use Find My iPhone to, well, find her iPhone. It was an easy way to check in and make sure everything was all right without interrupting her with a call or waiting for her to stop. Sometimes I'd even use Find My iPhone to display a message on her iPhone for the next time she pulled it out.
(The most annoying aspect of Find My iPhone is that MobileMe times out your login quickly, so if you want to check an hour later, you have to log in again, and the entire Web interface for that is fussy. Another annoyance is that Apple prevents you from accessing the Find My iPhone Web page from an iPhone, so once when we were meeting at friend's wedding party 55 miles away, I couldn't find her because I had only my iPhone for Internet access. It would have been helpful that time too, since she took a wrong turn and needed a pickup, but luckily there was sufficient cell service for a call to get through. Since then, I've discovered a workaround, detailed in "Use Find My iPhone from an iPhone," 2009-09-30.)
Before I hear any outraged gasps - how could I invade Tonya's privacy in this way! - let's be clear: she explicitly asked me to check up on her with Find My iPhone and made sure I knew her MobileMe password so I could log in to her account to do so. We're happily married and while we don't go poking into each other's computers on a regular basis, we're both entirely fine with the fact that the other should have full access to everything, just in case. I'd hope that's more the norm than the exception among married couples.
Tonya was much more comfortable biking long distances from home on rural roads knowing that I would be likely to find her if she broke down in an area with extremely minimal cell service, and she felt less anxious about real threats like drunken target practice and hotrodding pickup trucks, not to mention intangible fears like swamp monsters.
I wonder if this tension between wanting privacy and wanting certain people to know your whereabouts at any arbitrary time might be somewhat gender-based. As a guy, I don't often worry about making sure people know where I am when I go on long runs, and I'm not really afraid of anything out on the roads. But a number of the female athletes I know prefer to have someone know where they are when they're training alone, and if carrying an iPhone enables a spouse to check in from afar, that's a good thing.
I'd go further and suggest that Apple should open up Find My iPhone slightly, so you could give select people access to it without letting them into your entire MobileMe account. Of course, you'd have to be able to revoke those privileges easily too, and it should probably alert you whenever your location has been requested, and by whom.
Even better, Apple could make an iPhone app for Find My iPhone so you could use it easily while out and about with the people you trust. After all, if I'd had to go find Tonya 30 miles from home, it would be nice to be able to check easily if her location had changed from when I left the house, and in a scary accident scenario, I could see wanting updated location information quickly.
Another nice addition might be a Map My iPhone feature that would display your iPhone's location at user-specified intervals, again, only to those to whom you'd given access. Especially in rural upstate New York, where cell service is often poor or nonexistent, being able to see a last known location with a time stamp could be useful.
If you're looking for features along these lines now, AT&T does offer the service for locating your family's phones. It works with all AT&T phones, including the iPhone, though it doesn't take advantage of the iPhone's GPS capabilities and is thus limited to less-accurate cell tower trilateration. It costs $9.99 per month to locate two phones, or $14.99 per month for five phones.