We used it for our Disneymoon last year and really liked it. Like you, we already lived together and didn't really need anything, so we opted to register for honeymoon "extras" instead.
We put things in our registry that we didn't already have planned, so that if someone purchased it for us it truly would be an extra-special thing. Not everyone in my family was comfortable with using a honeymoon registry, but we did have some friends and family that used it. Because of their gifts, we were able to get a spa treatment on the last day of our honeymoon, spend some time at Disney Quest, go on a shopping spree at Downtown Disney, and have one more extra-special meal we hadn't planned on because it wasn't in our original budget.
I know some people choose to include things like their hotel stay and park tickets in the registry, and that's a great way to save money, too. However, like I said, we opted to put only extra-special items that were just a bit out of our budget. We thought it was easy to use and we were promptly notified via email when someone purchased something from our registry so we could thank them appropriately.