If you have more than one iOS device in the household, you've likely tried to wrap your head around the solution to get all your purchased apps, music, and other media available to ALL your devices. The Apple ID concept is abstract and definitely has its limitations, and iCloud introduces more haze to the picture. I'll try to set things straight by offering some tips I personally use.
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.
One Apple ID to rule them all (all apps and media that is)
The best way to get your purchases on all iOS devices is to use a shared Apple ID for them all. Create a family Apple ID if you're starting fresh, or designate the most used (or oldest) Apple ID as the king. Connecting each device to that shared Apple ID will allow all future purchases to be shared — apps, music, books, newsstand magazines, etc.
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...
If someone later decides they want a particular app, it's available in App Store under Purchases, but I personally didn't want my wife's app purchases and music popping up on my device and vice versa.
Get your own Cloud
With the media situation sorted out, now comes iCloud. iCloud allows the ability to sync your mail, contacts, calendar, bookmarks, reminders and more. You'll likely want to create a separate iCloud account for each person in your family to manage these services. This will keep contacts and calendars (among other features) separate for each individual — my contacts don't merge with my wife's and vice versa. This method is also helpful for Messaging, and Game Center — messages won't be broadcast over all iOS devices and Game Center progress won't be linked.
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)