We have used AAA to book the our last 2 trips to Disney. I find it well worth it, not only do you get a discount, but you also get extra perks.....for instance this year the perks are: commemorative luggage tags (1 per person), 5X7 photopass gift certificate, $15 gift certificate to dine @ Planet Hollywood, one round of minigolf, Watercraft rental discount, disney story time experience, and 40 page WDW how to guide. Also you get admission to AAA's hiden lounge in MK...where you get a free drink and can relax as long as you want, we took advantage of the lounge last time we were there to get out of a quick thunderstorm. Plus you also get a discount, just by using AAA to book our trip we saved approx $500 from the price we were quoted from the WDW website. Also you get to park in the AAA parking section @ WDW parks....which is close to the entrance....totally worth it.
Also you get discounts on all trips, not just Disney and they also do customized road maps (if you are going to go on a road trip you give them your destination and they make a customized road TripTik map for you....it is awesome we used it when we took a trip to Canada)
Overall I would totally recommend AAA.