Yep, the best advice is "you can't make everyone happy all the time". I've taken several large groups on various trips (snow skiing, cruises, beach, etc.). In the end, I've found it best if I set up the "major" reservation, e.g. the house, cruise, cabin, etc. After the basics, I think it is best, if you want to keep your sanity (and your friends :-), is to not be the group entertainment guide. I create excursions that I plan on doing, then I invite anyone else interested to join. Putting yourself in the position of "planning and organizing" everyone's activities will take up a lot of your time, and in the end, it is doubtful everyone will be happy. In other words, empower everyone to plan their own activities but offer them the option to join what you're doing.
Also, RCCL and CruiseCritic have teamed up to offer Cruise Critic Parties on board RCCL. You need 25 people to create a party, but they can be any 25 from the entire ship. For example, I have a group right now on a party. the party is 5 times the number of folks that I signed up. Check out RCCL's web site for details.