I have a sky caddie 2.5 and like it a lot. In fact, I am lost without it now, especially when playing a new course. The unit does keep score and will also work with a handicap index to give you a net score.
As dependant as I am on it, I could still enjoy a round with out it but really like having it. It helps primarily with club selection on approach shots. It will help you decide if you want to lay up or go for it on longer holes. All of this speeds up play and I am all for speeding up pace of play.
I am seriously looking for one to use with my iPhone. Mainly not for my home course but for going on vacation and playing on totally new courses. That's where I think I will need it.