I'm not a golfer, but I have seen a number of GPS devices that are aimed at the golfer. The goal of these devices is to give the golfer a better idea of the whole layout so they can play a better game.
I have always thought that a GPS device dedicated to golf alone would be hard to justify cost wise. Expresso has announced a new golf device that will be easier to justify for many users. The new GPs unit works for golfing and can be used in the car as well.
The device is called the AG1 and in addition to being a GPS device for the car and golf course, it is also a full portable media player. The device is the result of a partnership with Navigon and iGolf. It has a HD resolution screen, dual stereo speakers, automatic switching form portrait to landscape, 5-way mounting capabilities, and a 533MHz Samsung processor. Pricing and availability are unknown.