We've only done one ABD (Italy) and had a wonderful experience. For me the value came not only in the big things (like transferring the luggage when we changed hotels) to the little things (like showing us the "nicest" public toilets, giving us the coins to pay for them and providing extra tissue because the attendant only gave one square to each person).
We also did so many things we would not have done on our own - like going out on a boat to swim in the Mediterranean at Capri, making pizza on a farm where the chef had to motorbike out to the field to get more fresh basil, and biking around the walls of Lucca.
Our guides were so friendly and kind. One was from America and was from Italy. They worked so well together and took great care of us.
We never waiting in line for anything, never had to think about brining drinks or snacks on the bus, never worried about our safety and never had to plan a thing! I'm normally the vacation planner, so giving that up to someone else had me concerned, but in the end it made for an incredibly relaxing vacation. All we had to do was enjoy ourselves and leave our cares behind.
We haven't been able to do another ABD yet, but I'm sure we will at some point!