I like a little app for Google maps called latitude. I wouldn't be able to tell you the iPhone equivalent, I'm an Android user, I would think there would be something similar. latitude lets you share your location with your friends. We have kids away at school and it is fun to see almost real-time where they are.
We use Blogger to write up our trips after we enjoy them and so we have a record of what we did and places we've been as well. Sometimes my wife "checks in" using Facebook on her iPad when we are at the campground too.
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