If the "gps system" is linked with your county's GIS system it works great. Ours is not as of yet, have heard some scuddlebut about that possibly happening, but nothing concrete yet. Yes, mapbooks are still the best and a good knowledge of your run area.
Perfect example, 2-3 years ago one of the other crews left on a call (approx. 1 mile away). GPS took them to a town approximately 10 miles away and neither relized it until dispatch asked them what was taking so long. And then they had no idea how to get there and got turn by turn over dispatch, because they still refused to pick up a map book.
The call was for a local college student. The college wrote a lengthy letter about their displeasure of the experience.