I think the great thing about DU is that it doesn't cost any MORE for all the service they can provide. I used them for my last reservation, because I had a lot of family issues going on that made it difficult for me to keep up with all the discount possibilities. It was nice to know that someone was watching out for me. They emailed me right away when the AP codes came out and told me all the options I had. Although there weren't any AP codes at my chosen resort, and I decided to stick with the AAA discount instead of switching, they would have been ready, willing, and able to make any changes I wanted. They will not only make your ADR's for you, which is another big stress load you can get rid of, but they will work up a day by day itinerary for you. It's like having a personal assistant. The fact that you get all of this without paying anything extra is great, even if you end up paying rack rate (which, if they can't get you a discount for, you probably wouldn't have found a discount anywhere else either).
Would I use them all the time? Probably not. Not because I had a bad experience, but some of my trips are during hurricane season. I like knowing I can cancel if I need to, without taking any commission away from anyone. But would I ever use them again? Sure. I've already been thinking about it.