I've resisted commenting in all of these GPS threads before, but can't anymore.
I've been using a SkyCaddie for just past a year and a half. It has improved my game. I'm a low single-digit handicap, having cut my handicap by 3 shots since I started using it. Some of it is that I'm just playing better through practice than I was at the start of 2007, but some of it I can attribute to the GPS.
I can't say I'm good enough to hit it either 152 or 154, but where it has helped me is knowing not yardage just to middle of green, but knowing distance to the front edge when it's a front pin, and to the back of the green when it's a back pin. I CAN hit it different if I think it's 152 or 162. In other words, if it's a back pin and GPS shows I have 152 to back edge, I know I can hit my 150 yard club and not have to worry about going over. I'm generally a lousy judge of distances on the course, and this has helped me hit balls pin high a lot more than I used to. Regardless of having the distance, I still have to hit the shot, along with all the other shots where I don't use GPS (drives, chips, sand shots, putts).
Hasn't slowed my group down at all. Probably half of the guys in my group use SkyCaddie type devices. Our foursomes can walk in 3 1/2 hours at my course. It's real easy to be checking the distance as you walk up to your ball. Pull a club and hit.
Sure it's new technology. So are 460-cc heads, titanium, graphite, multi-layer balls, etc., etc.