That's what I concluded after migrating a friend's iTunes and iOS content, and navigating the chaotic intersection of Digital Rights Management (FairPlay), identity management, ownership identity, and Cloud vs. multi-device iTunes vs. multi-user OS X. Not to mention the MobileMe vs. iCloud migration.
Really, has anyone figured this out? I mean, I think I'm pretty good at this stuff, but we're talking combinatorial explosion here. Different rules for email, calendar, music, video, apps, across multiple identifies and platforms -- with no way to merge or reconcile multiple identities...
... Enter the Apple ID you want to use for iCloud in Apple () menu > System Preferences > iCloud. Enter the Apple ID you want to use for store purchases (including iTunes in the Cloud and iTunes Match) in iTunes > iTunes Store... 
... You cannot merge two or more Apple IDs into a single one...
... You can switch the Apple ID you use for store purchases at any time. However, you can only change the account you use for any iTunes in the Cloud features once every 90 days...
and (emphases mine)
... Your Apple ID can have up to 10 devices and computers (combined) associated with it. Each computer must also be authorized using the same Apple ID. Once a device or computer is associated with your Apple ID, you cannot associate that device or computer with another Apple ID for 90 days...
... : Removing a device from your Apple ID does not override the 90 day timer. The timer must complete 90 days from the day the device was associated before it can be associated to another Apple ID....
Only a post-singular AI could truly visualize all the options here.
It's fairly clear, however, where Apple wants us to go.
Today my family's five devices sync to one iTunes instance. Each devices has the same AppleID for store purchases, but different MobileMe identities. The family can share movies, apps, music and so on.  Mail and Calendars for each device go to the Cloud.
The future is quite different. There will be no more iTunes, no more shared media libraries, no more shared app libraries. Each iOS device will be associated with a single identity for both purchasing and iCloud services. (Though a child's identity may be associated with a parent's credit card, or purchases will be iTunes credit only.) OS X will become only a way to access Cloud media, and that access will be tied to identity as well.
My sympathy for piracy grows.
- fn -
 In reality, when I reviewed my friend's devices, it was not possible to set a different Apple ID for iCloud.
 Heaven knows what the licensing says we can do. Only some older music is DRMd.
- Apple IDs and iCloud
- iTunes Store: Associating a device or computer to your Apple ID
- Apple Scrambles To Merge Apple IDs To Stave Off iCloud Sync Mess | Epicenter | Wired.com 9/2011 -- they didn't manage the merge but there's a transitional role where the Apple ID and the MobileMe ID can live together for MobileMe users and perhaps even into iCloud. I'm going very slowly with my family's iCloud migration.
- Gordon's Notes: The sharing challenge: access, topic and identity. Why G+ fails. 11/2011 - a different sort of sharing problem
- Gordon's Tech: The multi-iPhone family - two approaches 7/2010 - the good old days.
- Gordon's Tech: Apple's identity and account system is screwed up. Again. 10/2008 - the .mac to .me transition stunk
More on the peculiar 90 day limit here. It seems to pertain to 'downloading past purchases' or iTunes Match. It applies to the entire computer rather than a user account. What a friggin' mess.
Update 2: More thoughts as I replay this post
- I wonder if the 90 day limit will eventually be a standard for transferring ownership of digital purchases. I can't find any information on how that duration was established.
- I suspect in a few years there will be a lot of digital material in the family repository that only I will be able to use. Ownership transfer would be "nice". Hacking FairPlay is more likely (eventually 2012 FairPlay should be pretty hackable).
- With Apple's new regime there are significant advantages to combining Apple hardware with Google and Amazon products. After all, they can't fit into Apple's model. In the new world we can't share our iBooks, but everyone can share Kindle books. A shared Apple identity may prevent use of iCloud, but it won't prevent use of gCloud.
- Curiously, this may mean the return of family night at the movies! Instead of sharing across multiple devices, we'll be back to sharing on a single device with a large screen.