I have a GPS III+ that I bought about three years ago. I have used it geocaching, hiking, driving, and even flying. (I’m a USAF C-141B Flight Engineer) Some of the features I had to have when I was looking for a GPS are, waterproof, detachable antenna, and the trackback function. I wanted waterproof because it rains here in Washington (state) a lot. I personally believe that the best day to go geocaching is when the weather is the worst. It just adds to the adventure. I had to have a detachable antenna to connect it to the aircraft antenna. I have no reception in the cockpit of the plane, even with the antenna pointing out the window. (However, on a commercial airline I have gotten great reception pointing the antenna that came with the unit out the side windows in the cabin. I have a suction-cup RAM mount and fasten it right to the window, I get all the satellites on that side of the plane. I do get funny looks from the cabin crew though and have had to put it away due to a particularly ignorant stewardess.) I may upgrade to the GPS V soon to get WAAS. Just my two cents……..