My family and I just started. We've been using the iPhone and app just to see if the kids (10, 5) are interested enough to invest in a Garmin. I think that's a definite yes. They have hit me up every day this week when I get home from work to go search for the caches in our neighborhood. So far, we've stuck with the 1-1.5 rating caches, and have had really good luck. Found four so far in five trips. iPhone map did not have a creek on a particular hunt so we got stuck. The iPhone gets a little jinky under trees, but it is workable. The nice thing about it is you can read the hints and logs right there at the spot to help find. And as someone else said, once you find a few, it begins to get easier. Hiding places sort of jump out at you as you get close.
