I definitely get the reasoning behind sharing an ID--I've done it myself before--but in the long run I feel like it's always more of a pain than it's worth, especially with iCloud syncing and managing who is syncing what where. (Think of all you can sync using iCloud: Mail, Contacts, Calendars, Bookmarks, Notes, Photos, Documents, etc; the more you get into the Apple ecosystem, the better it is to have your own Apple ID). Other than that, it's a great way to share apps, I agree!
I know you can use one ID for the App Store and another for other things, but to me (and of course it's just a personal opinion) I'd rather have a more unified account so I don't have to deal with multiple passwords, people forgetting passwords, the number of device authorizations, payment details, etc among different family members.