Yes, I have stayed in a concierge suite twice.
There will be a meeting on embarkation afternoon for the concierge guests and the staff will take care of ALL your reservations then...spa, Palo, wine tasting, etc. You can even sign the kids up for the children's programming at that time. They probably will not let you book more than one dinner or brunch but you can certainly book one of each, plus High Tea if you're so inclined.
As for other amenities, these include:
Daily contact from the concierge staff and little gifts such as fruit platters, cookies, etc
CDs and videos that you can check out
Full room-service breakfast available (except the last day of the cruise)
Menus from all restaurants with room-service dining available from those restaurants on the days they are serving the particular menus
Concierge staff to take care of any tips you want to charge to your account
Intital set-up of soda in the stateroom, it costs after that (at least for the Cat. 3s)
The main benefit is the extra space you get in the stateroom.
