Hey,
I just started Geocaching and have only been using my Iphone. What I have found is that it burns through the battery in a big hurry and once you hit the trees it loses the signal easily. But on the flip side I love it in the urban area and I always have it with me so I can Geocache on a whim. Having said all that I am going to purchase a GPS, probably a Garmin Oregon 400T, but then again I change my mind about 10 times a day on what to get based on the latest review I read:-)