I encountered the multiple iOS device puzzle when I upgraded to the new Retina display model, giving my first-generation iPad to my wife. We wanted access to the same music, same app purchases, and same digital magazines, but we also wanted to keep our own calendars, contacts, and customizations. Here's the solution that works for us.
The difficulty here, and it's a big one, is if you have devices that have been going along their merry way purchasing apps and music under separate Apple ID's. Unfortunately, there's no way to merge purchases from one Apple ID to another. So if this describes you, you're going to have to make a tough call. Give up all current app purchases for the convenience of having all new purchases synced across multiple devices? Or just keep doing things separately with no option to share new purchases? Maybe Apple will change policies or provide a better way to accomodate this in the future, but it doesn't seem likely.
If you do decide to go the unified Apple ID route, one more sanity tip would be to turn off auto downloads on devices for apps, music, and books. This is done in Settings -> Store...
Take a moment to think about each of the features and your likely use case to determine if this is a good approach for you and your family. I personally deviate from the separate iCloud accounts because it's just my wife and I at the house. Since we use Gmail and Google Calendar the iCloud services for mail, contacts, and calendars are redundant — so we disable those and just rely on the Google servers to manage. One shared iCloud account allows us to save recipes and fun links via the reading list and bookmark sync feature.
It's unfortunate that managing these items is so difficult. Hopefully, I've at least outlined some of the limitations to give you an idea of how to reign in your media the way you want — that way you can just use and enjoy your devices already.
(Images: Chris Perez)