Admittedly, the features that are packed into today's handheld GPS units are amazing. Then, of course, there are the practical limitations to using all those cool features while trapped out on a beach cat at 20 knots. Personally, I use a basic model, the Garmin 12. I've had it for six years and haven't found myself wanting for any additional functionality. (Unlike one of the higher priced models mentioned earlier in this thread, it displays VMG, too.) If I could modify the interface, though, I'd include easier to read screens with larger numbers.

I rarely use my GPS for anything other than recording the day's sailing. It's fun to see the max speed, or upload the tracks to my charting software, etc. While on the water, I tend to use basic piloting skills to navigate. (Beach cats are most always operated within sight of land, except perhaps when the fog rolls in.) Traditional piloting methods keep your head out of the boat and develop a better awareness of the surroundings.