Last year, Paul planned a trip to the Wisconsin Dells with 4 childhood friends and their families. He based the trip off of the movie Grownups, and we had such a good time, we did it again this year.
It was surprisingly easy, and since we stayed a giant house it gave every one their own space, while being able to come together for meals, and games, and general merriment.
A few tips:
Plan ahead. We didn't do this as well this year, but have times and places lined up. You can sometimes get a discount and otherwise, you spend a bunch of time trying to figure it all out during the vacation.
Each family was responsible for one meal and the clean up. This makes it so that everyone gets a break, and when it is your time to cook, it is really fun! (I had a hard time staying out of the kitchen, though.) Oh, and use a crock pot if you can.
Bring board games, art materials, bubbles, outdoor toys and put them in a community bin for kids to use as they please. (I always think no one will want to play with all the stuff I haul, but in the end, the kids loved it!) This game was a hit.
Have one evening for parents only game time. (This was the best part of the trip!) Paul made a 3 part game this year, with "How well do you know your spouse" questions, Girls vs Boys questions, and then the tie breaker of the Flour Game, which we totally did incorrectly.