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You guys are making this way to hard. Here is how it works. Me and my wife:
Under app store settins we both log in with the same account we have always shared for purchases (my MobileMe). Under the new iCloud settings we are each logged into a seperate account, mine being the MobileMe (well it will be when I can transfer it, for now I used a new dummy iCloud account), and hers is logged into a brand new iCloud account. Very simple, allows us to continue purchase sharing, but keep seperate contacts, calendars, etc on iCloud.